Windows Scripting to call other commands?

Windows Scripting to call other commands? - javascript

I was trying my hand at Windows shell scripting using cscript and Javascript. The idea was to take a really long Python command that I was tired of typing into the command line over and over. What I wanted to do was write a script that is much shorter to write the whole Python command into a Windows script and just call the Windows script, which would be a lot less to type. I just don't know how I would go about calling a "command within a command" if that makes sense.
This is probably an easy thing, but I'm an newbie at this so please bear with me!
The idea:
Example original command: python do <something really complicated with a long filepath>
Windows Script: cscript easycommand
<package id = "easycommand">
<job id = "main" >
<script type="text/javascript">
// WHAT GOES HERE TO CALL python do <something really complicated>
WScript.Echo("Success!");
</script>
</job>
</package>
Thanks for all your help!

Here's what I use
function logMessage(msg) {
if (typeof wantLogging != "undefined" && wantLogging) {
WScript.Echo(msg);
}
}
// http://msdn.microsoft.com/en-us/library/d5fk67ky(VS.85).aspx
var windowStyle = {
hidden : 0,
minimized : 1,
maximized : 2
};
// http://msdn.microsoft.com/en-us/library/a72y2t1c(v=VS.85).aspx
var specialFolders = {
windowsFolder : 0,
systemFolder : 1,
temporaryFolder : 2
};
function runShellCmd(command, deleteOutput) {
deleteOutput = deleteOutput || false;
logMessage("RunAppCmd("+command+") ENTER");
var shell = new ActiveXObject("WScript.Shell"),
fso = new ActiveXObject("Scripting.FileSystemObject"),
tmpdir = fso.GetSpecialFolder(specialFolders.temporaryFolder),
tmpFileName = fso.BuildPath(tmpdir, fso.GetTempName()),
rc;
logMessage("shell.Run("+command+")");
// use cmd.exe to redirect the output
rc = shell.Run("%comspec% /c " + command + "> " + tmpFileName,
windowStyle.Hidden, true);
logMessage("shell.Run rc = " + rc);
if (deleteOutput) {
fso.DeleteFile(tmpFileName);
}
return {
rc : rc,
outputfile : (deleteOutput) ? null : tmpFileName
};
}
Here's an example of how to use the above to list the Sites defined in IIS with Appcmd.exe:
var
fso = new ActiveXObject("Scripting.FileSystemObject"),
windir = fso.GetSpecialFolder(specialFolders.WindowsFolder),
r = runShellCmd("%windir%\\system32\\inetsrv\\appcmd.exe list sites");
if (r.rc !== 0) {
// 0x80004005 == E_FAIL
throw {error: "ApplicationException",
message: "shell.run returned nonzero rc ("+r.rc+")",
code: 0x80004005};
}
// results are in r.outputfile
var
textStream = fso.OpenTextFile(r.outputfile, OpenMode.ForReading),
sites = [], item,
re = new RegExp('^SITE "([^"]+)" \\((.+)\\) *$'),
parseOneLine = function(oneLine) {
// each line is like this: APP "kjsksj" (dkjsdkjd)
var tokens = re.exec(oneLine), parts;
if (tokens === null) {
return null;
}
// return the object describing the website
return {
name : tokens[1]
};
};
// Read from the file and parse the results.
while (!textStream.AtEndOfStream) {
item = parseOneLine(textStream.ReadLine()); // you create this...
logMessage(" site: " + item.name);
sites.push(item);
}
textStream.Close();
fso.DeleteFile(r.outputfile);

Well, basically:
Obtain a handle to the shell so you can execute your script
Create the command you want to execute (parameters and all) as a string
Call the Run method on the shell handle, and figure out which window mode you want and also whether you want to wait until the spawned process finishes (probably) or not.
Error handling because Run throws exceptions
At this point it's worth writing a lot of utility functions if ever you need to do it more than once:
// run a command, call: run('C:\Python27\python.exe', 'path/to/script.py', 'arg1', 'arg2') etc.
function run() {
try {
var cmd = "\"" + arguments[0] + "\"";
var arg;
for(var i=1; i< arguments.length; ++i) {
arg = "" + arguments[i];
if(arg.length > 0) {
cmd += arg.charAt(0) == "/" ? (" " + arg) : (" \"" + arg + "\"");
}
}
return getShell().Run(cmd, 1, true); // show window, wait until done
}
catch(oops) {
WScript.Echo("Error: unable to execute shell command:\n"+cmd+
"\nInside directory:\n" + pwd()+
"\nReason:\n"+err_message(oops)+
"\nThis script will exit.");
exit(121);
}
}
// utility which makes an attempt at retrieving error messages from JScript exceptions
function err_message(err_object) {
if(typeof(err_object.message) != 'undefined') {
return err_object.message;
}
if(typeof(err_object.description) != 'undefined') {
return err_object.description;
}
return err_object.name;
}
// don't create new Shell objects each time you call run()
function getShell() {
var sh = WScript.CreateObject("WScript.Shell");
getShell = function() {
return sh;
};
return getShell();
}
For your use case this may be sufficient, but you might want to extend this with routines to change working directory and so on.

Related

Read a text file into an array with OS X Javascript

I'm really struggling to find documentation on how to read a text file into an array using OS X Automation with Javascript.
Here's what I have so far:
var app = Application.currentApplication();
app.includeStandardAdditions = true;
var myFile = "/Users/Me/Dropbox/textfile.txt";
var openedFile = app.openForAccess(myfile, { writePermission: true });
var myText = openedFile.??
app.closeAccess(URLFile);
I copied most of this from the official Apple documentation. I'm finding it really difficult to find documentation anywhere online. For example, what are the arguments for openForAccess? There doesn't seem to be anything in any dictionary to describe that method.
Am I wasting my time with JXA?

Apple has an entire page devoted to reading and writing files in their Mac Automation Scripting Guide. This includes a function that performs exactly the action you are looking for. I've re-written your example below using the readAndSplitFile function from Apple's guide:
var app = Application.currentApplication()
app.includeStandardAdditions = true
function readAndSplitFile(file, delimiter) {
// Convert the file to a string
var fileString = file.toString()
// Read the file using a specific delimiter and return the results
return app.read(Path(fileString), { usingDelimiter: delimiter })
}
var fileContentsArray = readAndSplitFile('/Users/Me/Dropbox/textfile.txt', '\n')
After running the above code, fileContentsArray will hold an array of strings, with each string containg a single line of the file. (You could also use \t as a delimiter to break at every tab, or any other character of your choosing.)

Some generic functions and an illustrative test:
(function () {
'use strict';
// GENERIC FUNCTIONS ------------------------------------------------------
// doesFileExist :: String -> Bool
function doesFileExist(strPath) {
var error = $();
return $.NSFileManager.defaultManager
.attributesOfItemAtPathError($(strPath)
.stringByStandardizingPath, error), error.code === undefined;
};
// lines :: String -> [String]
function lines(s) {
return s.split(/[\r\n]/);
};
// readFile :: FilePath -> maybe String
function readFile(strPath) {
var error = $(),
str = ObjC.unwrap(
$.NSString.stringWithContentsOfFileEncodingError($(strPath)
.stringByStandardizingPath, $.NSUTF8StringEncoding, error)
),
blnValid = typeof error.code !== 'string';
return {
nothing: !blnValid,
just: blnValid ? str : undefined,
error: blnValid ? '' : error.code
};
};
// show :: a -> String
function show(x) {
return JSON.stringify(x, null, 2);
};
// TEST -------------------------------------------------------------------
var strPath = '~/DeskTop/tree.txt';
return doesFileExist(strPath) ? function () {
var dctMaybe = readFile(strPath);
return dctMaybe.nothing ? dctMaybe.error : show(lines(dctMaybe.just));
}() : 'File not found:\n\t' + strPath;
})();

Providing stdin to an emscripten HTML program?

I have a C program that takes one argument (a char array / string) via command line and also reads from stdin. I've compiled it to JavaScript using emscripten. This was successful and I can run it just like the normal C program using node.js:
emcc -O2 translate.c
node translate.js "foo" < bar.txt
As you can see, I'm providing the string "foo" as an argument and the contents of bar.txt as stdin. Now I want this to be a self-contained HTML file.
By changing the output to HTML:
emcc -O2 translate.c -o trans.html
I provide the argument by adding arguments: ['foo'], to the definitions in var Module. This works as expected, the program receives the argument correctly.
Now, how do I provide the stdin input to this program? I don't need to do this dynamically. It would be fine to just declare a string somewhere in the HTML with the required stdin content.

A way would be to use the Emscripten Filesystem API, for example by calling FS.init in the Module preRun function, passing custom functions to be used for standard input, output and error.
var Module = {
preRun: function() {
function stdin() {
// Return ASCII code of character, or null if no input
}
function stdout(asciiCode) {
// Do something with the asciiCode
}
function stderr(asciiCode) {
// Do something with the asciiCode
}
FS.init(stdin, stdout, stderr);
}
};
The functions are quite low-level: they each deal with one character at a time as an ASCII code. If you have strings you want to pass in, you would have to iterate over the characters of the string yourself. I suspect charCodeAt would be helpful. To output strings from stdout or stderr, then I suspect fromCharCode would be helpful.
Example (not very well tested!) implementations using each are below.
var input = "This is from the standard input\n";
var i = 0;
var Module = {
preRun: function() {
function stdin() {
if (i < res.length) {
var code = input.charCodeAt(i);
++i;
return code;
} else {
return null;
}
}
var stdoutBuffer = "";
function stdout(code) {
if (code === "\n".charCodeAt(0) && stdoutBuffer !== "") {
console.log(stdoutBuffer);
stdoutBuffer = "";
} else {
stdoutBuffer += String.fromCharCode(code);
}
}
var stderrBuffer = "";
function stderr(code) {
if (code === "\n".charCodeAt(0) && stderrBuffer !== "") {
console.log(stderrBuffer);
stderrBuffer = "";
} else {
stderrBuffer += String.fromCharCode(code);
}
}
FS.init(stdin, stdout, stderr);
}
};

Rather than editing the output of Emscripten, you could monkey patch the Window object
window.prompt = function() {
return 'This will appear to come from standard input';
};
Not wonderful, but I would deem this less of a hack than editing the Emscripten-generated Javascript.

According the question "Edit" , I made my function , thx a lot.
Just hope the code below can help someone else.
comment run(); in the end of emscript
// in my emscript
// shouldRunNow refers to calling main(), not run().
var shouldRunNow = true;
if (Module['noInitialRun']) {
shouldRunNow = false;
}
//run(); // << here
// {{POST_RUN_ADDITIONS}}
result = areaInput(); // As the question mentioned
add the code below in your html file to activate run() in emscript
<script>
var message;
var point = -1;
function getArea(){
message = document.getElementById('input').value.split('\n');
}
function areaInput(){
if(point >= message.length - 1){
return null;
}
point += 1;
return message[point];
}
function execEmscript(){
window.console = {
log: function(str){
document.getElementById("output").value += "\n" + str;
}
}
getArea();
run();
}
</script>
remember io textareas in your html
<textarea id="input" cols="80" rows="30"></textarea>
<textarea id="output" cols="80" rows="30"></textarea>
and a button
<button onclick="execEmscript();">run</button>

emscripten - string/char* parameter reference weirdness

So I'm playing around with emscripten and making linked lists. I started with the following code in C -
struct Node {
struct Node *next;
char *value;
};
extern struct Node *ll_new_node(char *value) {
struct Node *node;
node = malloc(sizeof(struct Node));
node->value = value;
return node;
}
extern struct Node *ll_add(struct Node *root, char *value) {
struct Node *node = ll_new_node(value);
if (root == NULL) {
root = node;
} else {
tail(root)->next = node;
}
return root;
}
//....
In the page I'm calling the code this way -
var new_node = Module.cwrap('ll_new_node', 'object', ['string'])
var add = Module.cwrap('ll_add', 'object', ['object', 'string']);
var list = 0;
Zepto(function($){
var printList = function() {
var node = list;
var s = "head -> ";
while (node != null && node != 0) {
s = s + value(node) + " -> ";
node = next(node);
}
s = s + "NULL";
$('#display').text(s);
};
printList();
$('#addBtn').on('click', function() {
var add_value = $('#itemField').val();
if (add_value && add_value.length > 0) {
list = add(list, add_value);
printList();
}
});
//...
});
What was happening was if I put "A" in the text box and added it to the list, "head -> A -> NULL" would print. Then if I but "B" in the text box and added it to the list, "head -> B -> B -> NULL" would print. The same pattern continued as more nodes were added. It was adding the new node, but it seems all node->value fields pointed to a shared string reference.
I made some test code in C to build and print a list, and it worked as expected with no changes. I ended up fixing it via emscripten by using strcpy on the string passed into ll_new_node and assigning the copy to node->value.
Is this "expected behavior" or a bug? Is the "copied reference" to the string due to some problem with how I'm using it on the JavaScript side? Is there some way to tell Emscripten not to do this?

A proper wrapper for console.log with correct line number?

I'm now developing an application, and place a global isDebug switch. I would like to wrap console.log for more convenient usage.
//isDebug controls the entire site.
var isDebug = true;
//debug.js
function debug(msg, level){
var Global = this;
if(!(Global.isDebug && Global.console && Global.console.log)){
return;
}
level = level||'info';
Global.console.log(level + ': '+ msg);
}
//main.js
debug('Here is a msg.');
Then I get this result in Firefox console.
info: Here is a msg. debug.js (line 8)
What if I want to log with line number where debug() gets called, like info: Here is a msg. main.js (line 2)?

This is an old question and All the answers provided are overly hackey, have MAJOR cross browser issues, and don't provide anything super useful. This solution works in every browser and reports all console data exactly as it should. No hacks required and one line of code Check out the codepen.
var debug = console.log.bind(window.console)
Create the switch like this:
isDebug = true // toggle this to turn on / off for global controll
if (isDebug) var debug = console.log.bind(window.console)
else var debug = function(){}
Then simply call as follows:
debug('This is happening.')
You can even take over the console.log with a switch like this:
if (!isDebug) console.log = function(){}
If you want to do something useful with that.. You can add all the console methods and wrap it up in a reusable function that gives not only global control, but class level as well:
var Debugger = function(gState, klass) {
this.debug = {}
if (gState && klass.isDebug) {
for (var m in console)
if (typeof console[m] == 'function')
this.debug[m] = console[m].bind(window.console, klass.toString()+": ")
}else{
for (var m in console)
if (typeof console[m] == 'function')
this.debug[m] = function(){}
}
return this.debug
}
isDebug = true //global debug state
debug = Debugger(isDebug, this)
debug.log('Hello log!')
debug.trace('Hello trace!')
Now you can add it to your classes:
var MyClass = function() {
this.isDebug = true //local state
this.debug = Debugger(isDebug, this)
this.debug.warn('It works in classses')
}

You can maintain line numbers and output the log level with some clever use of Function.prototype.bind:
function setDebug(isDebug) {
if (window.isDebug) {
window.debug = window.console.log.bind(window.console, '%s: %s');
} else {
window.debug = function() {};
}
}
setDebug(true);
// ...
debug('level', 'This is my message.'); // --> level: This is my message. (line X)
Taking it a step further, you could make use of the console's error/warning/info distinctions and still have custom levels. Try it!
function setDebug(isDebug) {
if (isDebug) {
window.debug = {
log: window.console.log.bind(window.console, 'log: %s'),
error: window.console.error.bind(window.console, 'error: %s'),
info: window.console.info.bind(window.console, 'info: %s'),
warn: window.console.warn.bind(window.console, 'warn: %s')
};
} else {
var __no_op = function() {};
window.debug = {
log: __no_op,
error: __no_op,
warn: __no_op,
info: __no_op
}
}
}
setDebug(true);
// ...
debug.log('wat', 'Yay custom levels.'); // -> log: wat: Yay custom levels. (line X)
debug.info('This is info.'); // -> info: This is info. (line Y)
debug.error('Bad stuff happened.'); // -> error: Bad stuff happened. (line Z)

I liked #fredrik's answer, so I rolled it up with another answer which splits the Webkit stacktrace, and merged it with #PaulIrish's safe console.log wrapper. "Standardizes" the filename:line to a "special object" so it stands out and looks mostly the same in FF and Chrome.
Testing in fiddle: http://jsfiddle.net/drzaus/pWe6W/
_log = (function (undefined) {
var Log = Error; // does this do anything? proper inheritance...?
Log.prototype.write = function (args) {
/// <summary>
/// Paulirish-like console.log wrapper. Includes stack trace via #fredrik SO suggestion (see remarks for sources).
/// </summary>
/// <param name="args" type="Array">list of details to log, as provided by `arguments`</param>
/// <remarks>Includes line numbers by calling Error object -- see
/// * http://paulirish.com/2009/log-a-lightweight-wrapper-for-consolelog/
/// * https://stackoverflow.com/questions/13815640/a-proper-wrapper-for-console-log-with-correct-line-number
/// * https://stackoverflow.com/a/3806596/1037948
/// </remarks>
// via #fredrik SO trace suggestion; wrapping in special construct so it stands out
var suffix = {
"#": (this.lineNumber
? this.fileName + ':' + this.lineNumber + ":1" // add arbitrary column value for chrome linking
: extractLineNumberFromStack(this.stack)
)
};
args = args.concat([suffix]);
// via #paulirish console wrapper
if (console && console.log) {
if (console.log.apply) { console.log.apply(console, args); } else { console.log(args); } // nicer display in some browsers
}
};
var extractLineNumberFromStack = function (stack) {
/// <summary>
/// Get the line/filename detail from a Webkit stack trace. See https://stackoverflow.com/a/3806596/1037948
/// </summary>
/// <param name="stack" type="String">the stack string</param>
if(!stack) return '?'; // fix undefined issue reported by #sigod
// correct line number according to how Log().write implemented
var line = stack.split('\n')[2];
// fix for various display text
line = (line.indexOf(' (') >= 0
? line.split(' (')[1].substring(0, line.length - 1)
: line.split('at ')[1]
);
return line;
};
return function (params) {
/// <summary>
/// Paulirish-like console.log wrapper
/// </summary>
/// <param name="params" type="[...]">list your logging parameters</param>
// only if explicitly true somewhere
if (typeof DEBUGMODE === typeof undefined || !DEBUGMODE) return;
// call handler extension which provides stack trace
Log().write(Array.prototype.slice.call(arguments, 0)); // turn into proper array
};//-- fn returned
})();//--- _log
This also works in node, and you can test it with:
// no debug mode
_log('this should not appear');
// turn it on
DEBUGMODE = true;
_log('you should', 'see this', {a:1, b:2, c:3});
console.log('--- regular log ---');
_log('you should', 'also see this', {a:4, b:8, c:16});
// turn it off
DEBUGMODE = false;
_log('disabled, should not appear');
console.log('--- regular log2 ---');

I found a simple solution to combine the accepted answer (binding to console.log/error/etc) with some outside logic to filter what is actually logged.
// or window.log = {...}
var log = {
ASSERT: 1, ERROR: 2, WARN: 3, INFO: 4, DEBUG: 5, VERBOSE: 6,
set level(level) {
if (level >= this.ASSERT) this.a = console.assert.bind(window.console);
else this.a = function() {};
if (level >= this.ERROR) this.e = console.error.bind(window.console);
else this.e = function() {};
if (level >= this.WARN) this.w = console.warn.bind(window.console);
else this.w = function() {};
if (level >= this.INFO) this.i = console.info.bind(window.console);
else this.i = function() {};
if (level >= this.DEBUG) this.d = console.debug.bind(window.console);
else this.d = function() {};
if (level >= this.VERBOSE) this.v = console.log.bind(window.console);
else this.v = function() {};
this.loggingLevel = level;
},
get level() { return this.loggingLevel; }
};
log.level = log.DEBUG;
Usage:
log.e('Error doing the thing!', e); // console.error
log.w('Bonus feature failed to load.'); // console.warn
log.i('Signed in.'); // console.info
log.d('Is this working as expected?'); // console.debug
log.v('Old debug messages, output dominating messages'); // console.log; ignored because `log.level` is set to `DEBUG`
log.a(someVar == 2) // console.assert
Note that console.assert uses conditional logging.
Make sure your browser's dev tools shows all message levels!

Listen McFly, this was the only thing that worked for me:
let debug = true;
Object.defineProperty(this, "log", {get: function () {
return debug ? console.log.bind(window.console, '['+Date.now()+']', '[DEBUG]')
: function(){};}
});
// usage:
log('Back to the future');
// outputs:
[1624398754679] [DEBUG] Back to the future
The beauty is to avoid another function call like log('xyz')()
or to create a wrapper object or even class. Its also ES5 safe.
If you don't want a prefix, just delete the param.
update included current timestamp to prefix every log output.

Chrome Devtools lets you achieve this with Blackboxing. You can create console.log wrapper that can have side effects, call other functions, etc, and still retain the line number that called the wrapper function.
Just put a small console.log wrapper into a separate file, e.g.
(function() {
var consolelog = console.log
console.log = function() {
// you may do something with side effects here.
// log to a remote server, whatever you want. here
// for example we append the log message to the DOM
var p = document.createElement('p')
var args = Array.prototype.slice.apply(arguments)
p.innerText = JSON.stringify(args)
document.body.appendChild(p)
// call the original console.log function
consolelog.apply(console,arguments)
}
})()
Name it something like log-blackbox.js
Then go to Chrome Devtools settings and find the section "Blackboxing", add a pattern for the filename you want to blackbox, in this case log-blackbox.js

From: How to get JavaScript caller function line number? How to get JavaScript caller source URL?
the Error object has a line number property(in FF). So something like this should work:
var err = new Error();
Global.console.log(level + ': '+ msg + 'file: ' + err.fileName + ' line:' + err.lineNumber);
In Webkit browser you have err.stack that is a string representing the current call stack. It will display the current line number and more information.
UPDATE
To get the correct linenumber you need to invoke the error on that line. Something like:
var Log = Error;
Log.prototype.write = function () {
var args = Array.prototype.slice.call(arguments, 0),
suffix = this.lineNumber ? 'line: ' + this.lineNumber : 'stack: ' + this.stack;
console.log.apply(console, args.concat([suffix]));
};
var a = Log().write('monkey' + 1, 'test: ' + 2);
var b = Log().write('hello' + 3, 'test: ' + 4);

A way to keep line number is here: https://gist.github.com/bgrins/5108712. It more or less boils down to this:
if (Function.prototype.bind) {
window.log = Function.prototype.bind.call(console.log, console);
}
else {
window.log = function() {
Function.prototype.apply.call(console.log, console, arguments);
};
}
You could wrap this with isDebug and set window.log to function() { } if you aren't debugging.

You can pass the line number to your debug method, like this :
//main.js
debug('Here is a msg.', (new Error).lineNumber);
Here, (new Error).lineNumber would give you the current line number in your javascript code.

If you simply want to control whether debug is used and have the correct line number, you can do this instead:
if(isDebug && window.console && console.log && console.warn && console.error){
window.debug = {
'log': window.console.log,
'warn': window.console.warn,
'error': window.console.error
};
}else{
window.debug = {
'log': function(){},
'warn': function(){},
'error': function(){}
};
}
When you need access to debug, you can do this:
debug.log("log");
debug.warn("warn");
debug.error("error");
If isDebug == true, The line numbers and filenames shown in the console will be correct, because debug.log etc is actually an alias of console.log etc.
If isDebug == false, no debug messages are shown, because debug.log etc simply does nothing (an empty function).
As you already know, a wrapper function will mess up the line numbers and filenames, so it's a good idea to prevent using wrapper functions.

Stack trace solutions display the line number but do not allow to click to go to source, which is a major problem. The only solution to keep this behaviour is to bind to the original function.
Binding prevents to include intermediate logic, because this logic would mess with line numbers. However, by redefining bound functions and playing with console string substitution, some additional behaviour is still possible.
This gist shows a minimalistic logging framework that offers modules, log levels, formatting, and proper clickable line numbers in 34 lines. Use it as a basis or inspiration for your own needs.
var log = Logger.get("module").level(Logger.WARN);
log.error("An error has occured", errorObject);
log("Always show this.");
EDIT: gist included below
/*
* Copyright 2016, Matthieu Dumas
* This work is licensed under the Creative Commons Attribution 4.0 International License.
* To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/
*/
/* Usage :
* var log = Logger.get("myModule") // .level(Logger.ALL) implicit
* log.info("always a string as first argument", then, other, stuff)
* log.level(Logger.WARN) // or ALL, DEBUG, INFO, WARN, ERROR, OFF
* log.debug("does not show")
* log("but this does because direct call on logger is not filtered by level")
*/
var Logger = (function() {
var levels = {
ALL:100,
DEBUG:100,
INFO:200,
WARN:300,
ERROR:400,
OFF:500
};
var loggerCache = {};
var cons = window.console;
var noop = function() {};
var level = function(level) {
this.error = level<=levels.ERROR ? cons.error.bind(cons, "["+this.id+"] - ERROR - %s") : noop;
this.warn = level<=levels.WARN ? cons.warn.bind(cons, "["+this.id+"] - WARN - %s") : noop;
this.info = level<=levels.INFO ? cons.info.bind(cons, "["+this.id+"] - INFO - %s") : noop;
this.debug = level<=levels.DEBUG ? cons.log.bind(cons, "["+this.id+"] - DEBUG - %s") : noop;
this.log = cons.log.bind(cons, "["+this.id+"] %s");
return this;
};
levels.get = function(id) {
var res = loggerCache[id];
if (!res) {
var ctx = {id:id,level:level}; // create a context
ctx.level(Logger.ALL); // apply level
res = ctx.log; // extract the log function, copy context to it and returns it
for (var prop in ctx)
res[prop] = ctx[prop];
loggerCache[id] = res;
}
return res;
};
return levels; // return levels augmented with "get"
})();

Here's a way to keep your existing console logging statements while adding a file name and line number or other stack trace info onto the output:
(function () {
'use strict';
var isOpera = !!window.opera || navigator.userAgent.indexOf(' OPR/') >= 0;
var isChrome = !!window.chrome && !!window.chrome.webstore;
var isIE = /*#cc_on!#*/false || !!document.documentMode;
var isEdge = !isIE && !!window.StyleMedia;
var isPhantom = (/PhantomJS/).test(navigator.userAgent);
Object.defineProperties(console, ['log', 'info', 'warn', 'error'].reduce(function (props, method) {
var _consoleMethod = console[method].bind(console);
props[method] = {
value: function MyError () {
var stackPos = isOpera || isChrome ? 2 : 1;
var err = new Error();
if (isIE || isEdge || isPhantom) { // Untested in Edge
try { // Stack not yet defined until thrown per https://learn.microsoft.com/en-us/scripting/javascript/reference/stack-property-error-javascript
throw err;
} catch (e) {
err = e;
}
stackPos = isPhantom ? 1 : 2;
}
var a = arguments;
if (err.stack) {
var st = err.stack.split('\n')[stackPos]; // We could utilize the whole stack after the 0th index
var argEnd = a.length - 1;
[].slice.call(a).reverse().some(function(arg, i) {
var pos = argEnd - i;
if (typeof a[pos] !== 'string') {
return false;
}
if (typeof a[0] === 'string' && a[0].indexOf('%') > -1) { pos = 0 } // If formatting
a[pos] += ' \u00a0 (' + st.slice(0, st.lastIndexOf(':')) // Strip out character count
.slice(st.lastIndexOf('/') + 1) + ')'; // Leave only path and line (which also avoids ":" changing Safari console formatting)
return true;
});
}
return _consoleMethod.apply(null, a);
}
};
return props;
}, {}));
}());
Then use it like this:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<script src="console-log.js"></script>
</head>
<body>
<script>
function a () {
console.log('xyz'); // xyz (console-log.html:10)
}
console.info('abc'); // abc (console-log.html:12)
console.log('%cdef', "color:red;"); // (IN RED:) // def (console-log.html:13)
a();
console.warn('uuu'); // uuu (console-log.html:15)
console.error('yyy'); // yyy (console-log.html:16)
</script>
</body>
</html>
This works in Firefox, Opera, Safari, Chrome, and IE 10 (not yet tested on IE11 or Edge).

The idea with bind Function.prototype.bind is brilliant. You can also use npm library lines-logger. It shows origin source files:
Create logger anyone once in your project:
var LoggerFactory = require('lines-logger').LoggerFactory;
var loggerFactory = new LoggerFactory();
var logger = loggerFactory.getLoggerColor('global', '#753e01');
Print logs:
logger.log('Hello world!')();

With modern javascript and the use of getters, you could write something like this:
window.Logger = {
debugMode: true,
get info() {
if ( window.Logger.debugMode ) {
return window.console.info.bind( window.console );
} else {
return () => {};
}
}
}
The nice part about it is that you can have both static and computed values printed out, together with correct line numbers. You could even define multiple logger with different settings:
class LoggerClz {
name = null;
debugMode = true;
constructor( name ) { this.name = name; }
get info() {
if ( this.debugMode ) {
return window.console.info.bind( window.console, 'INFO', new Date().getTime(), this.name );
} else {
return () => {};
}
}
}
const Logger1 = new LoggerClz( 'foo' );
const Logger2 = new LoggerClz( 'bar' );
function test() {
Logger1.info( '123' ); // INFO 1644750929128 foo 123 [script.js:18]
Logger2.info( '456' ); // INFO 1644750929128 bar 456 [script.js:19]
}
test();

A little variation is to to have debug() return a function, which is then executed where you need it - debug(message)(); and so properly shows the correct line number and calling script in the console window, while allowing for variations like redirecting as an alert, or saving to file.
var debugmode='console';
var debugloglevel=3;
function debug(msg, type, level) {
if(level && level>=debugloglevel) {
return(function() {});
}
switch(debugmode) {
case 'alert':
return(alert.bind(window, type+": "+msg));
break;
case 'console':
return(console.log.bind(window.console, type+": "+msg));
break;
default:
return (function() {});
}
}
Since it returns a function, that function needs to be executed at the debug line with ();. Secondly, the message is sent to the debug function, rather than into the returned function allowing pre-processing or checking that you might need, such as checking log-level state, making the message more readable, skipping different types, or only reporting items meeting the log level criteria;
debug(message, "serious", 1)();
debug(message, "minor", 4)();

You can use optional chaining to really simplify this. You get full access to the console object with no hacks and concise syntax.
const debug = (true) ? console : null;
debug?.log('test');
debug?.warn('test');
debug?.error('test')
If debug == null, everything after the ? is ignored with no error thrown about inaccessible properties.
const debug = (false) ? console : null;
debug?.error('not this time');
This also lets you use the debug object directly as a conditional for other debug related processes besides logging.
const debug = (true) ? console : null;
let test = false;
function doSomething() {
test = true;
debug?.log('did something');
}
debug && doSomething();
if (debug && test == false) {
debug?.warn('uh-oh');
} else {
debug?.info('perfect');
}
if (!debug) {
// set up production
}
If you want, you can override the various methods with a no-op based on your desired log level.
const debug = (true) ? console : null;
const quiet = true; const noop = ()=>{};
if (debug && quiet) {
debug.info = noop;
debug.warn = noop;
}
debug?.log('test');
debug?.info('ignored in quiet mode');
debug?.warn('me too');

//isDebug controls the entire site.
var isDebug = true;
//debug.js
function debug(msg, level){
var Global = this;
if(!(Global.isDebug && Global.console && Global.console.log)){
return;
}
level = level||'info';
return 'console.log(\'' + level + ': '+ JSON.stringify(msg) + '\')';
}
//main.js
eval(debug('Here is a msg.'));
This will give me info: "Here is a msg." main.js(line:2).
But the extra eval is needed, pity.

I have been looking at this issue myself lately. Needed something very straight forward to control logging, but also to retain line numbers. My solution is not looking as elegant in code, but provides what is needed for me. If one is careful enough with closures and retaining.
I've added a small wrapper to the beginning of the application:
window.log = {
log_level: 5,
d: function (level, cb) {
if (level < this.log_level) {
cb();
}
}
};
So that later I can simply do:
log.d(3, function(){console.log("file loaded: utils.js");});
I've tested it of firefox and crome, and both browsers seem to show console log as intended. If you fill like that, you can always extend the 'd' method and pass other parameters to it, so that it can do some extra logging.
Haven't found any serious drawbacks for my approach yet, except the ugly line in code for logging.

This implementation is based on the selected answer and helps reduce the amount of noise in the error console: https://stackoverflow.com/a/32928812/516126
var Logging = Logging || {};
const LOG_LEVEL_ERROR = 0,
LOG_LEVEL_WARNING = 1,
LOG_LEVEL_INFO = 2,
LOG_LEVEL_DEBUG = 3;
Logging.setLogLevel = function (level) {
const NOOP = function () { }
Logging.logLevel = level;
Logging.debug = (Logging.logLevel >= LOG_LEVEL_DEBUG) ? console.log.bind(window.console) : NOOP;
Logging.info = (Logging.logLevel >= LOG_LEVEL_INFO) ? console.log.bind(window.console) : NOOP;
Logging.warning = (Logging.logLevel >= LOG_LEVEL_WARNING) ? console.log.bind(window.console) : NOOP;
Logging.error = (Logging.logLevel >= LOG_LEVEL_ERROR) ? console.log.bind(window.console) : NOOP;
}
Logging.setLogLevel(LOG_LEVEL_INFO);

Here's my logger function (based on some of the answers). Hope someone can make use of it:
const DEBUG = true;
let log = function ( lvl, msg, fun ) {};
if ( DEBUG === true ) {
log = function ( lvl, msg, fun ) {
const d = new Date();
const timestamp = '[' + d.getHours() + ':' + d.getMinutes() + ':' +
d.getSeconds() + '.' + d.getMilliseconds() + ']';
let stackEntry = new Error().stack.split( '\n' )[2];
if ( stackEntry === 'undefined' || stackEntry === null ) {
stackEntry = new Error().stack.split( '\n' )[1];
}
if ( typeof fun === 'undefined' || fun === null ) {
fun = stackEntry.substring( stackEntry.indexOf( 'at' ) + 3,
stackEntry.lastIndexOf( ' ' ) );
if ( fun === 'undefined' || fun === null || fun.length <= 1 ) {
fun = 'anonymous';
}
}
const idx = stackEntry.lastIndexOf( '/' );
let file;
if ( idx !== -1 ) {
file = stackEntry.substring( idx + 1, stackEntry.length - 1 );
} else {
file = stackEntry.substring( stackEntry.lastIndexOf( '\\' ) + 1,
stackEntry.length - 1 );
}
if ( file === 'undefined' || file === null ) {
file = '<>';
}
const m = timestamp + ' ' + file + '::' + fun + '(): ' + msg;
switch ( lvl ) {
case 'log': console.log( m ); break;
case 'debug': console.log( m ); break;
case 'info': console.info( m ); break;
case 'warn': console.warn( m ); break;
case 'err': console.error( m ); break;
default: console.log( m ); break;
}
};
}
Examples:
log( 'warn', 'log message', 'my_function' );
log( 'info', 'log message' );

For Angular / Typescript console logger with correct line number you can do the following:
example file: console-logger.ts
export class Log {
static green(title: string): (...args: any) => void {
return console.log.bind(console, `%c${title}`, `background: #222; color: #31A821`);
}
static red(title: string): (...args: any) => void {
return console.log.bind(console, `%c${title}`, `background: #222; color: #DA5555`);
}
static blue(title: string): (...args: any) => void {
return console.log.bind(console, `%c${title}`, `background: #222; color: #5560DA`);
}
static purple(title: string): (...args: any) => void {
return console.log.bind(console, `%c${title}`, `background: #222; color: #A955DA`);
}
static yellow(title: string): (...args: any) => void {
return console.log.bind(console, `%c${title}`, `background: #222; color: #EFEC47`);
}
}
Then call it from any other file:
example file: auth.service.ts
import { Log } from 'path to console-logger.ts';
const user = { user: '123' }; // mock data
Log.green('EXAMPLE')();
Log.red('EXAMPLE')(user);
Log.blue('EXAMPLE')(user);
Log.purple('EXAMPLE')(user);
Log.yellow('EXAMPLE')(user);
It will look like this in the console:
Stackblitz example

I found some of the answers to this problem a little too complex for my needs. Here is a simple solution, rendered in Coffeescript. It'a adapted from Brian Grinstead's version here
It assumes the global console object.
# exposes a global 'log' function that preserves line numbering and formatting.
(() ->
methods = [
'assert', 'clear', 'count', 'debug', 'dir', 'dirxml', 'error',
'exception', 'group', 'groupCollapsed', 'groupEnd', 'info', 'log',
'markTimeline', 'profile', 'profileEnd', 'table', 'time', 'timeEnd',
'timeStamp', 'trace', 'warn']
noop = () ->
# stub undefined methods.
for m in methods when !console[m]
console[m] = noop
if Function.prototype.bind?
window.log = Function.prototype.bind.call(console.log, console);
else
window.log = () ->
Function.prototype.apply.call(console.log, console, arguments)
)()

Code from http://www.briangrinstead.com/blog/console-log-helper-function:
// Full version of `log` that:
// * Prevents errors on console methods when no console present.
// * Exposes a global 'log' function that preserves line numbering and formatting.
(function () {
var method;
var noop = function () { };
var methods = [
'assert', 'clear', 'count', 'debug', 'dir', 'dirxml', 'error',
'exception', 'group', 'groupCollapsed', 'groupEnd', 'info', 'log',
'markTimeline', 'profile', 'profileEnd', 'table', 'time', 'timeEnd',
'timeStamp', 'trace', 'warn'
];
var length = methods.length;
var console = (window.console = window.console || {});
while (length--) {
method = methods[length];
// Only stub undefined methods.
if (!console[method]) {
console[method] = noop;
}
}
if (Function.prototype.bind) {
window.log = Function.prototype.bind.call(console.log, console);
}
else {
window.log = function() {
Function.prototype.apply.call(console.log, console, arguments);
};
}
})();
var a = {b:1};
var d = "test";
log(a, d);

window.line = function () {
var error = new Error(''),
brower = {
ie: !-[1,], // !!window.ActiveXObject || "ActiveXObject" in window
opera: ~window.navigator.userAgent.indexOf("Opera"),
firefox: ~window.navigator.userAgent.indexOf("Firefox"),
chrome: ~window.navigator.userAgent.indexOf("Chrome"),
safari: ~window.navigator.userAgent.indexOf("Safari"), // /^((?!chrome).)*safari/i.test(navigator.userAgent)?
},
todo = function () {
// TODO:
console.error('a new island was found, please told the line()\'s author(roastwind)');
},
line = (function(error, origin){
// line, column, sourceURL
if(error.stack){
var line,
baseStr = '',
stacks = error.stack.split('\n');
stackLength = stacks.length,
isSupport = false;
// mac版本chrome(55.0.2883.95 (64-bit))
if(stackLength == 11 || brower.chrome){
line = stacks[3];
isSupport = true;
// mac版本safari(10.0.1 (12602.2.14.0.7))
}else if(brower.safari){
line = stacks[2];
isSupport = true;
}else{
todo();
}
if(isSupport){
line = ~line.indexOf(origin) ? line.replace(origin, '') : line;
line = ~line.indexOf('/') ? line.substring(line.indexOf('/')+1, line.lastIndexOf(':')) : line;
}
return line;
}else{
todo();
}
return '😭';
})(error, window.location.origin);
return line;
}
window.log = function () {
var _line = window.line.apply(arguments.callee.caller),
args = Array.prototype.slice.call(arguments, 0).concat(['\t\t\t#'+_line]);
window.console.log.apply(window.console, args);
}
log('hello');
here was my solution about this question. when you call the method: log, it will print the line number where you print your log

The way I solved it was to create an object, then create a new property on the object using Object.defineProperty() and return the console property, which was then used as the normal function, but now with the extended abilty.
var c = {};
var debugMode = true;
var createConsoleFunction = function(property) {
Object.defineProperty(c, property, {
get: function() {
if(debugMode)
return console[property];
else
return function() {};
}
});
};
Then, to define a property you just do...
createConsoleFunction("warn");
createConsoleFunction("log");
createConsoleFunction("trace");
createConsoleFunction("clear");
createConsoleFunction("error");
createConsoleFunction("info");
And now you can use your function just like
c.error("Error!");

Based on other answers (mainly #arctelix one) I created this for Node ES6, but a quick test showed good results in the browser as well. I'm just passing the other function as a reference.
let debug = () => {};
if (process.argv.includes('-v')) {
debug = console.log;
// debug = console; // For full object access
}

Nothing here really had what I needed so I add my own approach: Overriding the console and reading the original error line from a synthetic Error. The example stores the console warns and errors to console.appTrace, having errors very detailed and verbose; in such way that simple (console.appTrace.join("") tells me all I need from the user session.
Note that this works as of now only on Chrome
(function () {
window.console.appTrace = [];
const defaultError = console.error;
const timestamp = () => {
let ts = new Date(), pad = "000", ms = ts.getMilliseconds().toString();
return ts.toLocaleTimeString("cs-CZ") + "." + pad.substring(0, pad.length - ms.length) + ms + " ";
};
window.console.error = function () {
window.console.appTrace.push("ERROR ",
(new Error().stack.split("at ")[1]).trim(), " ",
timestamp(), ...arguments, "\n");
defaultError.apply(window.console, arguments);
};
const defaultWarn = console.warn;
window.console.warn = function () {
window.console.appTrace.push("WARN ", ...arguments, "\n");
defaultWarn.apply(window.console, arguments);
};
})();
inspired by Get name and line of calling function in node.js and date formatting approach in this thread.

This is what worked for me. It creates a new object with all the functionality of the original console object and retains the console object.
let debugOn=true; // we can set this from the console or from a query parameter, for example (&debugOn=true)
const noop = () => { }; // dummy function.
const debug = Object.create(console); // creates a deep copy of the console object. This retains the console object so we can use it when we need to and our new debug object has all the properties and methods of the console object.
let quiet = false;
debug.log = (debugOn) ? debug.log : noop;
if (debugOn&&quiet) {
debug.info = noop;
debug.warn = noop;
debug.assert = noop;
debug.error = noop;
debug.debug = noop;
}
console.log(`we should see this with debug off or on`);
debug.log(`we should not see this with debugOn=false`);

All the solutions here dance around the real problem -- the debugger should be able to ignore part of the stack to give meaningful lines. VSCode's js debugger can now do this. At the time of this edit, the feature is available via the nightly build of the js-debug extension. See the link in the following paragraph.
I proposed a feature for VSCode's debugger here that ignores the top of the stack that resides in any of the skipFiles file paths of the launch configuration. The property is in the launch.json config of your vscode workspace. So you can create a file/module responsible for wrapping console.log, add it to the skipFiles and the debugger will show the line that called into your skipped file rather than console.log itself.
It is in the nightly build of the js-debug extension. It looks like it could be in the next minor release of visual studio code. I've verified it works using the nightly build. No more hacky workarounds, yay!

let debug = console.log.bind(console);
let error = console.error.bind(console);
debug('debug msg');
error('more important message');
Reading for noobs:
bind (function): https://www.w3schools.com/js/js_function_bind.asp
chrome console (object): https://developer.mozilla.org/en-US/docs/Web/API/console
function: https://www.w3schools.com/js/js_functions.asp
object: https://www.w3schools.com/js/js_objects.asp

Create Firefox Addon to Watch and modify XHR requests & reponses

Update: I guess the subject gave a wrong notion that I'm looking for an existing addon. This is a custom problem and I do NOT want an existing solution.
I wish to WRITE (or more appropriately, modify and existing) Addon.
Here's my requirement:
I want my addon to work for a particular site only
The data on the pages are encoded using a 2 way hash
A good deal of info is loaded by XHR requests, and sometimes
displayed in animated bubbles etc.
The current version of my addon parses the page via XPath
expressions, decodes the data, and replaces them
The issue comes in with those bubblified boxes that are displayed
on mouse-over event
Thus, I realized that it might be a good idea to create an XHR
bridge that could listen to all the data and decode/encode on the fly
After a couple of searches, I came across nsITraceableInterface[1][2][3]
Just wanted to know if I am on the correct path. If "yes", then kindly
provide any extra pointers and suggestions that may be appropriate;
and if "No", then.. well, please help with correct pointers :)
Thanks,
Bipin.
[1]. https://developer.mozilla.org/en/NsITraceableChannel
[2]. http://www.softwareishard.com/blog/firebug/nsitraceablechannel-intercept-http-traffic/
[3]. http://www.ashita.org/howto-xhr-listening-by-a-firefox-addon/

nsITraceableChannel is indeed the way to go here. the blog posts by Jan Odvarko (softwareishard.com) and myself (ashita.org) show how to do this. You may also want to see http://www.ashita.org/implementing-an-xpcom-firefox-interface-and-creating-observers/, however it isn't really necessary to do this in an XPCOM component.
The steps are basically:
Create Object prototype implementing nsITraceableChannel; and create observer to listen to http-on-modify-request and http-on-examine-response
register observer
observer listening to the two request types adds our nsITraceableChannel object into the chain of listeners and make sure that our nsITC knows who is next in the chain
nsITC object provides three callbacks and each will be called at the appropriate stage: onStartRequest, onDataAvailable, and onStopRequest
in each of the callbacks above, our nsITC object must pass on the data to the next item in the chain
Below is actual code from a site-specific add-on I wrote that behaves very similarly to yours from what I can tell.
function TracingListener() {
//this.receivedData = [];
}
TracingListener.prototype =
{
originalListener: null,
receivedData: null, // array for incoming data.
onDataAvailable: function(request, context, inputStream, offset, count)
{
var binaryInputStream = CCIN("#mozilla.org/binaryinputstream;1", "nsIBinaryInputStream");
var storageStream = CCIN("#mozilla.org/storagestream;1", "nsIStorageStream");
binaryInputStream.setInputStream(inputStream);
storageStream.init(8192, count, null);
var binaryOutputStream = CCIN("#mozilla.org/binaryoutputstream;1",
"nsIBinaryOutputStream");
binaryOutputStream.setOutputStream(storageStream.getOutputStream(0));
// Copy received data as they come.
var data = binaryInputStream.readBytes(count);
//var data = inputStream.readBytes(count);
this.receivedData.push(data);
binaryOutputStream.writeBytes(data, count);
this.originalListener.onDataAvailable(request, context,storageStream.newInputStream(0), offset, count);
},
onStartRequest: function(request, context) {
this.receivedData = [];
this.originalListener.onStartRequest(request, context);
},
onStopRequest: function(request, context, statusCode)
{
try
{
request.QueryInterface(Ci.nsIHttpChannel);
if (request.originalURI && piratequesting.baseURL == request.originalURI.prePath && request.originalURI.path.indexOf("/index.php?ajax=") == 0)
{
var data = null;
if (request.requestMethod.toLowerCase() == "post")
{
var postText = this.readPostTextFromRequest(request, context);
if (postText)
data = ((String)(postText)).parseQuery();
}
var date = Date.parse(request.getResponseHeader("Date"));
var responseSource = this.receivedData.join('');
//fix leading spaces bug
responseSource = responseSource.replace(/^\s+(\S[\s\S]+)/, "$1");
piratequesting.ProcessRawResponse(request.originalURI.spec, responseSource, date, data);
}
}
catch (e)
{
dumpError(e);
}
this.originalListener.onStopRequest(request, context, statusCode);
},
QueryInterface: function (aIID) {
if (aIID.equals(Ci.nsIStreamListener) ||
aIID.equals(Ci.nsISupports)) {
return this;
}
throw Components.results.NS_NOINTERFACE;
},
readPostTextFromRequest : function(request, context) {
try
{
var is = request.QueryInterface(Ci.nsIUploadChannel).uploadStream;
if (is)
{
var ss = is.QueryInterface(Ci.nsISeekableStream);
var prevOffset;
if (ss)
{
prevOffset = ss.tell();
ss.seek(Ci.nsISeekableStream.NS_SEEK_SET, 0);
}
// Read data from the stream..
var charset = "UTF-8";
var text = this.readFromStream(is, charset, true);
// Seek locks the file so, seek to the beginning only if necko hasn't read it yet,
// since necko doesn't seek to 0 before reading (at lest not till 459384 is fixed).
if (ss && prevOffset == 0)
ss.seek(Ci.nsISeekableStream.NS_SEEK_SET, 0);
return text;
}
else {
dump("Failed to Query Interface for upload stream.\n");
}
}
catch(exc)
{
dumpError(exc);
}
return null;
},
readFromStream : function(stream, charset, noClose) {
var sis = CCSV("#mozilla.org/binaryinputstream;1", "nsIBinaryInputStream");
sis.setInputStream(stream);
var segments = [];
for (var count = stream.available(); count; count = stream.available())
segments.push(sis.readBytes(count));
if (!noClose)
sis.close();
var text = segments.join("");
return text;
}
}
hRO = {
observe: function(request, aTopic, aData){
try {
if (typeof Cc == "undefined") {
var Cc = Components.classes;
}
if (typeof Ci == "undefined") {
var Ci = Components.interfaces;
}
if (aTopic == "http-on-examine-response") {
request.QueryInterface(Ci.nsIHttpChannel);
if (request.originalURI && piratequesting.baseURL == request.originalURI.prePath && request.originalURI.path.indexOf("/index.php?ajax=") == 0) {
var newListener = new TracingListener();
request.QueryInterface(Ci.nsITraceableChannel);
newListener.originalListener = request.setNewListener(newListener);
}
}
} catch (e) {
dump("\nhRO error: \n\tMessage: " + e.message + "\n\tFile: " + e.fileName + " line: " + e.lineNumber + "\n");
}
},
QueryInterface: function(aIID){
if (typeof Cc == "undefined") {
var Cc = Components.classes;
}
if (typeof Ci == "undefined") {
var Ci = Components.interfaces;
}
if (aIID.equals(Ci.nsIObserver) ||
aIID.equals(Ci.nsISupports)) {
return this;
}
throw Components.results.NS_NOINTERFACE;
},
};
var observerService = Cc["#mozilla.org/observer-service;1"]
.getService(Ci.nsIObserverService);
observerService.addObserver(hRO,
"http-on-examine-response", false);
In the above code, originalListener is the listener we are inserting ourselves before in the chain. It is vital that you keep that info when creating the Tracing Listener and pass on the data in all three callbacks. Otherwise nothing will work (pages won't even load. Firefox itself is last in the chain).
Note: there are some functions called in the code above which are part of the piratequesting add-on, e.g.: parseQuery() and dumpError()

Tamper Data Add-on. See also the How to Use it page

You could try making a Greasemonkey script and overwriting the XMLHttpRequest.
The code would look something like:
function request () {
};
request.prototype.open = function (type, path, block) {
GM_xmlhttpRequest({
method: type,
url: path,
onload: function (response) {
// some code here
}
});
};
unsafeWindow.XMLHttpRequest = request;
Also note that you can turn a GM script into an addon for Firefox.

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