Develop Reference

Calling javascript functions in windbg breakpoint-commands

I have a windbg-issue concerning the execution
of a javascript-function as a breakpoint-command.
This observation was made in windbg Preview 10.0.17030.1002
and also in recent versions of windbg
when debugging a native x86 C++ program on Windows 10.
Test Setup
In my javascript-file dbg_test.js I have the following function:
function test()
{
var ctl = host.namespace.Debugger.Utility.Control;
host.diagnostics.debugLog(">>> Test\n");
ctl.ExecuteCommand("g");
}
In windbg, I load the javascript-provider, load my dbg_test.js script
and define a breakpoint-command to call this javascript-function:
bs 0 "dx #$scriptContents.test()"
Expected Behavior
The string ">>> Test" is shown in the output-pane of the command-window
everytime when breakpoint 0 is hit.
The debugger resumes execution.
Observed Behavior
The output ">>> Test" is shown only the first time
when breakpoint 0 is hit.
Subsequently hitting breakpoint 0 does not
produce any output.
Remarks
1) Doing the analogous test with "old style" windbg-commands works fine:
bs 0 ".printf \">>> Test\\n\\n\";g;"
but only after ending and restarting windbg
2) The same behavior is shown when I move the code of function "test" to the function "invokeScript()" and define the breakpoint-command via
bs 0 ".scriptrun d:\\dbg_scripts\\dbg_test.js"
3) Running the script from the windbg-command-line works.
4) Calling javascript-functions as in the test-scenario above worked in previous versions of windbg.
5) It seems that the statement
ctl.ExecuteCommand("g");
is the crucial one: If I comment out this statement, then the breakpoint
is hit every time and the output from
host.diagnostics.debugLog(">>> Test\n");
is shown on each hit of the breakpoint.
Of course, I have to resume the execution manually by pressing F5 or entering the command "g"
Questions
Can someone reproduce this issue ?
Is it legal to use javascript-functions in this way or am I doing something wrong here ?
Your feedback is greatly appreciated!
Kind/Best regards!

I ran into the same problem as you did. I was able to somewhat bypass the problem by declaring a script global variable
var lines = [];
and pushing log messages to this array rather than debug printing them:
lines.push(">>> Test");
In order to see the lines, I created a function
function print_lines() {
for (var line of lines) {
host.diagnostics.debugLog(line + "\n");
}
lines = [];
}
which I called from the prompt like so
dx #$scriptContents.print_lines();
I know that this is not really answering your question, but it might still be helpful for someone else that faces the same problem.

Google Scripts/Basic JavaScript - Issue fixed by debugger

I'm working on a Google Scripts add on for Google Sheets, but I'm trying to get the script working before I actually set it up on the sheet. The code below works fine if I set a breakpoint somewhere in the extractNumbers function. If I just execute the code without breakpoints, I get an error:
TypeError: Cannot call method "replace" of undefined. (line 36, file "")
Here's the code:
var myVar = phoneCheck("a1","a2","o1","o2");
Logger.log(myVar);
function phoneCheck(newCell,newHome,oldCell,oldHome) {
Logger.clear();
var newCell = extractNumbers(newCell);
var oldCell = extractNumbers(oldCell);
var newHome = extractNumbers(newHome);
var oldHome = extractNumbers(oldHome);
if (newCell === oldCell) {
return newCell;
exit;
} else if (newCell === oldHome && newHome === oldCell) {
return oldCell;
exit;
}
if (newCell === '' && oldCell !== '' ) {
return oldCell;
exit;
}
if (newCell !== oldCell && newCell !== oldHome) {
return newCell;
exit;
}
return "No value found";
exit;
}
function extractNumbers(input) {
Logger.log(input);
var str = input;
return str.replace( /\D+/g, '');
}
Now I realize my if/then logic is more than a bit inelegant, but for my purposes, quick and dirty is fine. I just need it to run.
ALSO, I have read of other novice JavaScript programmers having similar issues related to the sequence of code execution. If someone would like to link to a concise source aimed at a non-advanced audience, that would be great too. Thanks!
EDIT: I put my code into a new fiddle and it works fine, but it continues to fail in Google Scripts editor unless running in debug mode with a breakpoint. The problem seems to be that the function parameters aren't available to the function unless there is a breakpoint. Anyone have access to Google Scripts that can try my updated code from https://jsfiddle.net/hrzqg64L/ ?

None of the suggestions got to the root of your problem - and neither did your answer, although you've avoided the problem by putting an enclosure around everything.
There's no AJAX, no asynchronous behavior - it's simpler than that. "Shadowing of parameters" is likewise a red herring. Bad coding practice, yes - but not a factor here.
If someone would like to link to a concise source aimed at a non-advanced audience, that would be great too.
Sorry - no such thing. I can explain what's going on, but can't guarantee it will be accessible to novices.
The exception
Let's just clarify what causes the exception, or thrown error, that you've observed.
As written, extractNumbers() will throw an exception if it has a null parameter (or any non-string parameter) passed to it. If you choose to extractNumbers() then hit "run", you'll get:
TypeError: Cannot call method "replace" of undefined. (line 36, file "")
That is telling you that on line 36, which is return str.replace( /\D+/g, '');, the variable str contains an object that is undefined (...and has no replace() method).
For bullet-proof code, you would check your parameter(s) to ensure they are valid, and handle them appropriately. Sometimes that would be with a valid default, and other times you might return an error or throw an exception that is more explicit about the parameter problems.
Running code in Google's debugger
The only way to run code in Google's Debugger is to select a function, then choose "run" or "debug". Assuming you posted all your code, you had just two functions to choose from:
phoneCheck()
extractNumbers()
Whenever Google Apps Script runs any part of a script, the entire script is loaded and scanned to find all symbols & check syntax. The scope of all symbols is noted as well, and so are any dependencies between functions and global symbols (symbols outside of any closure, or block of code).
That takes some time. To speed things up when asked to execute a specific function, the global symbols are only evaluated if they are a dependency for the requested function or the functions it may call. There is another condition that will trigger evaluation of global symbols, and that is if there is a possibility that the debugger may need to stop and display values.
When this happens, any code that is outside a closure (outside a function, for example) will be executed. This is what you observed when you set breakpoints.
Why did it work when breakpoints were set?
As explained, just having a breakpoint set triggers evaluation of global symbols.
You start this script with a few lines of code that are not in any closure:
var myVar = phoneCheck("a1","a2","o1","o2");
Logger.log(myVar);
It is that code which makes the only proper invocation of phoneCheck() with parameters. Because myVar is evaluated, phoneCheck() gets called with parameters, and in turn calls extractNumbers() with a defined parameter.
Unfortunately, because of the way the debugger works, you cannot choose to run that code yourself. You need to rely on these side-effect behaviors.
How to fix this?
Simple. Don't rely on global code to invoke functions under test. Instead, write an explicit test function, and call that.
function test_phoneCheck() {
var myVar = phoneCheck("a1","a2","o1","o2");
Logger.log(myVar);
}

Finally found the issue, but I don't fully understand it.
This question got me thinking about scope and how it might be different in the Google Script environment. I figured a simple workaround would be to enclose the entire script in its own void function, and it worked! Also, I simplified the script quite a bit with an array:
function init () {
var numberArray = ["a3", "a2", "o3", "o10"];
var myVar = phoneCheck(numberArray);
Logger.log(myVar);
function phoneCheck(myArray) {
var phoneString = '';
Logger.clear();
var arrayLength = myArray.length;
for (i = 0; i < arrayLength; i++) {
phoneString += myArray[i].replace(/\D+/g, '');
}
return phoneString;
}
}
Also, I realize the functionality of this script is different than the original, but I was really just trying to solve this problem. Now that I have, I can finish the script properly.
Thanks for all the suggestions, everyone! I learned a lot of good things, even though they turned out not to be the answer.

Issue with retrieving object data on IE 8 on Windows XP or 2003

This is an interesting problem that I am facing with JavaScript and IE8 on Windows XP and Windows 2003. I create an object on the page and then retrive information about that object (for example, its version). When trying to get the version, I am running this code:
var myObject = document.getElementById(objectId);
console.log(myObject.version);
What is interesting is that this code works on every single browser except IE8 on Windows XP and 2003. I've done some debugging and this is where things get interesting.
myObject is not null but myObject.version is undefined. So what I did is I added an alert in between so the code is now as follows:
var myObject = document.getElementById(objectId);
alert(myObject.version);
console.log(myObject.version);
The alert results in "undefined", however, the console.log is now resulting in the actual version. If I add an alert before this alert of anything (let's say alert("something")) then the second alert has the actual version now. I am assuming this is a timing issue (for some reason the object needs sometime to be able to provide the data stored in it?) but I am not sure what kind of timing issue this is or how to approach it.
Sorry for the long description but any help is appreciated.

document.getElementById doesn't return an object. It returns a DOM element. So, you expect to see a .version property in a DOM element, which by the official W3C specification is missing (or at least I don't know about this).
I'm not sure what you are expecting to see in .version, but if it is something custom then you should create a custom object like that:
var o = { version: "..." }
console.log(o);
You said that this may be a time issue. If that's true then I'll suggest to try to access the .version property after the DOM is fully loaded. You can use jQuery for the purpose:
$(document).ready(function() {
var myObject = document.getElementById(objectId);
alert(myObject.version);
console.log(myObject.version);
});
You can add a setTimeout in your function till the .version property is there.
var f = function(callback) {
var check = function() {
var myObject = document.getElementById(objectId);
alert(myObject.version);
console.log(myObject.version);
if(typeof myObject.version !== "undefined") {
callback(myObject.version);
} else {
setTimeout(check, 1000);
}
}
setTimeout(check, 1000);
}

What happens if you put the <script>...</script> tag with the js code at the end of the html file? In my opinion, the code is executed when the DOM is not ready. If you put it in the end, then it will be executed after it's loaded.

This object constructor is preventing my script from running

I'm working on a project (creating a browser based check list). One of my goals has been to write every piece by hand without a library like jquery or a mysql database.
Currently I'm trying to create on object for managing tasks. I'm not finished the primary function, but everything is closed, and I don't detect any errors. Furthermore, I'm haven't iterated it or called it's functions yet, so there's nothing to reference it yet. When I comment it out, the script runs normally.
I've included the xml request links up above and tested them successfully in a separate portion of the script.
I'm testing in firefox.
I'm writing this in SciTE
Here's the code:
function Task(name,node,childNode,divClass,content,onclick)
{
function retrieveTask(node,childNode)
{
var taskArray = [];
taskArray.push(xmlDoc.getElementsByTagName(name)[node].childNodes[childNode].nodeValue;)
taskArray.push(xmlDoc.getElementsByTagName(description)[node].childNodes[childNode].nodeValue;)
taskArray.push(xmlDoc.getElementsByTagName(complete)[node].childNodes[childNode].nodeValue;)
return taskArray;
}
function displayTask(name,content)
{
var task = retrieveTask(node,childNode);
var clickDiv = "";
formatDiv(name,"task",task[1],clickDiv);
task[2] === true ? formatDiv(name+1,"incompleteBox"," ",clickDiv) : formatDiv(name+1,"completeBox","O",clickDiv);
}
}
If anyone could give me some insight or tips that would be awesome. This isn't homework, it's a hobby, so it's a self teaching process.

...childNodes[childNode].nodeValue;)
should be );

Running multiple Javascript scripts only when certain HTML elements exist?

Here's the situation. I'm building a site which uses lots of scripts looking somewhat like this:
function getRandomArrayIndex(source_array) {
return Math.floor(Math.random() * source_array.length);
}
function getRandomArrayEntry(source_array) {
var random_index = getRandomArrayIndex(source_array);
return source_array[random_index];
}
function getRandomBlah() {
var blahs = [
["A"],
["B"],
["C"],
["D"],
["E"],
["F"],
["G"],
["H"],
["I"],
["L"],
["M"],
["N"],
["O"],
["P"],
["R"],
["S"],
["T"],
["V"],
["W"],
["Y"],
]; var random_blah = getRandomArrayEntry(blahs);
return random_blah;
}
function displayBlah(blah) {
const TEXT_ROW = 0;
const LINK_ROW = 1;
var blah_text = blah[TEXT_ROW];
var blah_link = blah[LINK_ROW]; if (blah_link != null) {
document.getElementById("blah").innerHTML = '' + blah_text + '';
} else {
document.getElementById("blah").innerHTML = blah_text;
}
}
function generateRandomBlah(){
var random_blah = getRandomBlah();
displayBlah(random_blah);
}
And this will, when called with <body onload="generateRandomBlah()">, insert one of the letters at random into <span id="blah"></span>.
So there's about 15 of these scripts, each with their own functions named slightly differently for different uses - generateRandomBlah2, etc, with a corresponding different place in the HTML for each script to do its work.
Because I'm not a very good coder, the way the whole thing works is that in the 'body onload' tag, there's about 15 different 'generateRandomBlah()' functions just within this one tag. The nature of the site means that on any one page, I will only need 2 or 3 of these scripts at once, but I require the ability to call any of them on any page. As you can see, my current tactic is to just call them all at once, and if the corresponding doesn't exist for a script, it'll just ignore that fact and move onto the next one.
Except that it doesn't ignore the fact that there's no corresponding <span>.
As soon as one isn't present, the rest of the scripts break and don't actually do what they're supposed to do. Looking at the code in Chrome's 'inspect code' shows an error at the first script which happens to break: "Uncaught TypeError: Cannot set property 'innerHTML' of null". I see a couple of potential solutions, but I might be completely off:
1) Add some code into each script which tells it that, if there's no <span id> on the page to insert its code, it ends gracefully and moves onto the next one - gradually (obviously in less than a second speed-wise) going through the scripts and only running them if actually exists. (As you can see, the problem is that a script will get 'snagged' on the fact that there's no place to insert its code and doesn't just end gracefully if that happens.
2) Get rid of the 'onload' stuff and just make each script self-containing, calling its own function. I don't know if this would fix the problem, though.
Anyway, some help would be much appreciated, as I'm stumped.

As you said in your first solution, testing for null before trying to "do" anything is probably your best bet short of completely recoding.
function getRandomArrayIndex(source_array) {
if(source_array === null) return; // similar lines in each function should fix everything
return Math.floor(Math.random() * source_array.length);
}
That said, a much better approach than your current solution of making a bunch of very similar functions and running them all is to create a single function that can take parameters indicating what it should be doing. If they really are quite similar, it shouldn't be difficult and will result in a lot fewer lines of code. It would also be nice if you can find a way for your page to not call all of the functions every time, though with fixing the null pointers that's a much smaller issue.

Not sure if I'm missing something here, but since even the error message complains about the value being null the obvious solution is to check for null:
var element = document.getElementById("blah");
if( element !== null ) {
element.innerHTML = '' + blah_text + '';
}
If you need to do that often you can make a function for it:
function updateIfExists( id, content ) {
var element = document.getElementById( id );
if( element !== null ) {
element.innerHTML = content;
}
}
updateIfExists( 'blah', '' + blah_text + '' );