Variable cannot be changed inside Window object

Variable cannot be changed inside Window object - javascript

I'm developing a cordova app and within it, I'm using an iFrame. I'm using the following code to communicate between the iFrame and the app itself:
var eventMethod = window.addEventListener ? "addEventListener" : "attachEvent";
var eventer = window[eventMethod];
var messageEvent = eventMethod == "attachEvent" ? "onmessage" : "message";
var message = "";
var output = "";
eventer(messageEvent, function(e) {
message = e.data;
var data = JSON.parse(message);
for (var i = 0; i < data.messages.length; i++){
var msg = data.messages[i];
output = msg.msg;
alert(output); //*1
}
}, false);
I'm copying the code from here: https://davidwalsh.name/window-iframe
The alert inside the eventer at *1 show the output variable is what I want. But once outside of this eventer function, the variable output reverts to blank.
After some research I think it might because I'm creating a Window object, but I'm not sure if that's the case or exactly what it is.
How can I permenently modify the variable "output"? Thanks.

Try changing the for loop to this:
for (var i = 0; i < data.messages.length; i++){
var dataMsg = data.messages[i].msg;
output = dataMsg; alert(output); //*1
}
I don't know if there is an issue with assigning msg.msg to output.

The problem is with your understanding of how events work.
Judging from your comments, this is how you think it works:
// Ordering
var output = ""; // 1. Assign empty string to output
eventer(messageEvent, function(e) {
// assign value to output // 2. Assign value to output
});
alert(output); // 3. Print output
In reality, it works like this:
var output = ""; // 1. Assign empty string to output
eventer(messageEvent, function(e) {
// assign value to output // 3. Assign value to output
});
alert(output); // 2. Print output
The value is changed by your callback function, but you are accessing it in the wrong order. eventer, or in modern browsers, .addEventListener, registers a callback function. Your callback function will only get triggered after the current thread is finished. Of course it will print out an empty value, since alert is executed before you even changed its value.
If you are not familiar with the basics of event-based programming, I suggest you to take a look at this tutorial.
Just a side note, never use an iframe unless you have specific reasons of doing so. And also you do not need the first few lines since you are using Cordova. attachEvent is IE-specific.
As a general advice, try not to pollute the global scope with unnecessary variables in the future.

Related

Continue executing a dom command

I use this dom command in some testing pages:
document.querySelector('div#summary-item div.description').innerHTML || ""
But in some pages when the first part does not exist I don't receive the second "" but I receive this error and my programm stops
Uncaught TypeError: Cannot read property 'innerHTML' of null(…)
Is there any simple way to receive the "" without the need to use the typeof in an if statement?

You don't need typeof but you do need an if statement or some other flow control.
var el = document.querySelector('div#summary-item div.description');
var data = "";
if (el)
data = el.innerHTML;
Or here it is using the conditional operator:
var el = document.querySelector('div#summary-item div.description');
var data = el ? el.innerHTML : "";
Technically, you could get away without using a flow control statement or expression by using an object that has a .innerHTML property.
var data = (document.querySelector('div#summary-item div.description') || {innerHTML:""}).innerHTML;
But I think that's ugly. if statements are part of the language. Not sure why you'd want to avoid it.
Of course, you could always use a function that abstracts it away if it really bothers you.
function htmlFromElem(selector) {
var el = document.querySelector(selector);
return el ? el.innerHTML : "";
}
Then use it like this:
var data = htmlFromElem('div#summary-item div.description')

How to dynamically change the contents of a function using JavaScript

To help understand this the function is in the html page and it is generated, I cannot change the generated code:
function Update_qu7260() {
var newVal = ''
for( var idx = 0; idx < 2; idx++ )
{
var test
if( idx == 0 ) test = text7263
else if( idx == 1 ) test = text7265
if( test.matchObj ) newVal += test.leftSel + "-" + test.matchObj.rightSel + ","
}
newVal = newVal.substring( 0, newVal.length-1 )
VarQuestion_0001.set( newVal )
qu7260.hasBeenProcessed=false;
doImmFeedback('qu7260');
}
var qu7260 = new Object();
...
qu7260.updFunc = Update_qu7260;
var qObj=[qu7260];
Note in the above the number "7260", the numbers start at 1 so there are lots of them and each Update_###() will be different so I cannot re-write them with "hard wired" code. My code is in an external JavaScript file and is executed onLoad:
...
var updFunc = qObj[0].updFunc.toString();
if(updFunc.indexOf('doImmFeedback(')!=-1){
updFunc = updFunc.replace('doImmFeedback','doImmQuestionFeedback'); // do my function
updFunc = updFunc.replace('function ',''); // remove the word function
var funcName = updFunc.substr(0,updFunc.indexOf('(')); // get the function name e.g. Update_qu7260
updFunc = "window['" + funcName + "']=function" + updFunc.replace(funcName,'');
eval(updFunc);
}
...
When I change the eval() to alert() I can see the that it's correct, however, the eval() is not raising any errors and my function doImmQuestionFeedback is not being called. When I subsequently do an alert(qObj[0].updFunc.toString()) I see the original function.
It would seem that I have provided information that is too complex, so the following code is a better example:
function hi(){alert('hi');}
function changeHi(){
hi(); // I get an alert box with hi
newHi = "function hi(){alert('hi there');}"
eval(newHi);
hi(); // I get an alert box with hi
window.setTimeout('hi()',500); // I get an alert box with hi
}
window.setTimeout('changeHi()',500);
The following is the original question:
I have a predefined function that I did not create, however, I know it's name so I can get the function itself and then I change it by doing:
var funcText = window.updateFunc.toString();
funcText = funcText.replace('doSomeOtherFunction(','doMyFunction(');
How do I update the actual function so it will do all that it did before except it will now call doMyFuntion()?
The following is an example to help visualize what I want to do, the actual function I need to change is very complex. I have:
function updateFunc(whatToUpdate,true){
... - do lots of stuff.
var retVal = doSomeOtherFunction(whatToUdate);
... - do lots of stuff based on retVal
}
I need to change this to:
function updateFunc(whatToUpdate,true){
... - do lots of stuff
var retVal = doMyFunction(whatToUdate);
... - do lots of stuff based on retVal, I have had a chance to change retVal
}
Then the first thing my function will do is call doSomeOtherFunction() check/change the returned value and subsequently return the value to the updateFunc().
I have tried to manipulate the funcText above to:
funcText = 'window.updateFunc = function(...';
eval(funcText);
Without success.

This may be closed enough to what you are looking for.
Assuming you have this original function:
function originalFunc(val) {
// this function converts input string to upper case
return val.toUpperCase();
}
Now you want to override it to something either before or after you execute that function (in this example, we execute before, of course before or after doesn't matter in this case).
// we preserve orignal function
var originalFunc_save = originalFunc;
// now we override the original function with this block
var originalFunc = function(text) {
// lets call the orignal function
text = originalFunc_save(text);
// now do our custom thing
return text.split('').reverse().join('');
}
So our test should work.
var text = 'This is a test';
console.log(originalFunc(text));
Output:
TSET A SI SIHT
This method also works if you have to override functions inside a class. The only thing we have to be careful of is to choose a saved name that doesn't interfere with the original class code. _save may not be good enough, but you get the idea.
UPDATE: I'm updating this code above to use a string variable pointing to the original function. I think this is what the OP wanted.
Original code which defined by some library
function originalFunc(val) {
// this function converts input string to upper case
return val.toUpperCase();
}
Now we use the func string variable to point to that function and execute it.
var text = 'This is a test';
var func = 'originalFunc';
text = window[func](text);
console.log(text);
Output: Of course we get the original intended result because we haven't overridden it.
THIS IS A TEST
Now we write our code to override the original function behavior using a string pointing to the function.
// let's define a new function string
var funcSaved = func + '___saved';
// now preserve the original function code
window[funcSaved] = window[func];
// override the original function code block
window[func] = function(text) {
// lets call the orignal function
text = window[funcSaved](text);
// now do our custom thing
return text.split('').reverse().join('');
}
// let's test the code
text = 'This is a test';
text = window[func](text);
console.log(text);
Output:
TSET A SI SIHT

You can make a clone of updateFunc function, edit it at your discretion and work with it in what follows.
function updateFunc(whatToUpdate, param){ // the initial function
...
var retVal = doSomeOtherFunction(whatToUpdate);
return retVal;
}
// formation of unnamed function as string
var newfunc = updateFunc.toString().replace('function updateFunc', 'function ').replace('doSomeOtherFunction(', 'doMyFunction(');
function doMyFunction(whatToUpdate){ // your new function, just for example
console.log(parseInt(whatToUpdate) * 10);
}
var newUpdateFunc;
// declaring new version of 'updateFunc' function
// which is stored in 'newUpdateFunc' variable
eval("newUpdateFunc = " + newfunc);
newUpdateFunc(3); // outputs '30'

I believe this is a valid use case for the forgotten JavaScript with feature.
Basic idea: you call original updateFunc supplying your own version of doSomeOtherFunction to it using with namespace injection:
function updateFunc(whatToUpdate,true){
... - do lots of stuff.
var retVal = doSomeOtherFunction(whatToUdate);
... - do lots of stuff based on retVal
}
function patchUpdateFunc() {
var original_doSomeOtherFunction = window.doSomeOtherFunction;
var original_updateFunc = window.updateFunc;
function doMyFunction() {
// call original_doSomeOtherFunction() here,
// do your own stuff here.
};
window.updateFunc = function() {
with ({doSomeOtherFunction: doMyFunction}) {
return original_updateFunc.apply(this, arguments);
}
}
}
patchUpdateFunc();

I think you are going at this way too complicated.
If you only have doMyFunction and doSomeOtherFunction to switch between, you could just create a flag somewhere telling you to use one or the other when used in an if-statement.
If you want to call a function with a name you do not know beforehand and you only get a name during runtime, you could either accept the function to call as a parameter or accept the name of the function as a parameter and call it like so: var retVal = window[functionName](); (assuming functionName is a property of the window object).
I would highly recommend directly accepting a function as a parameter since the function may not be defined in a global scope.
EDIT:
After your clarification, I think, I can give you a satisfying answer:
if you have a string like var functionString = "function updateFunc(whatToUpdate){var retVal = doMyFunction(whatToUpdate);}";
You can define a function using a Function object:
window.updateFunc = new Function("whatToUpdate", "return (" + functionString + ")(whatToUpdate)");
This will replace the already existing function and you can give it any valid function string you want as long as you know and specify the arguments.

If I understood correctly, you want to override the external function. You can achieve that with the following code
//Someone else's function
function externalFunction(foo){
return "some text";
}
//Your function
function myFunction(value){
//Do something
}
//Override
var externalFunction = (function(){
var original = externalFunction; //Save original function
return function(){
var externalFunctionReturnValue = original.apply(this, arguments);
return myFunction(externalFunctionReturnValue);
}
})();
I strongly sugest not to use eval, but since you want to parse javascript from string:
function hi(){alert('hi');}
function changedHi(){
hi(); // I get an alert box with hi
newHi = "window['hi'] = function(){alert('hi there');}"
eval(newHi);
hi(); // I get an alert box with hi there
window.setTimeout('hi()',500); // I get an alert box with hi there
}
window.setTimeout('changedHi()',500);
UPDATE:
This code snippet works which is your original code:
<script type="text/javascript">
function doImmFeedback(foo){
console.log("DoImmFeedback: " + foo);
}
function Update_qu7260() {
console.log("Some code")
doImmFeedback('qu7260');
}
</script>
<script type="text/javascript">
var qu7260 = new Object();
qu7260.updFunc = Update_qu7260;
var qObj=[qu7260];
var updFunc = qObj[0].updFunc.toString();
if(updFunc.indexOf('doImmFeedback(')!=-1){
updFunc = updFunc.replace('doImmFeedback','doImmQuestionFeedback'); // do my function
updFunc = updFunc.replace('function ',''); // remove the word function
var funcName = updFunc.substr(0,updFunc.indexOf('(')); // get the function name e.g. Update_qu7260
updFunc = "window['" + funcName + "']=function" + updFunc.replace(funcName,'');
console.log(updFunc);
eval(updFunc);
}
function doImmQuestionFeedback(foo){
//Your function
console.log("doImmQuestionFeedback: " + foo);
}
Update_qu7260(); //This executes your doImmQuestionFeedback
</script>
So if your function isn't running, your function isn't in the global scope, or something else is happening, and we can't know if don't have any more info. Check your developer's console for javascript errors.

Function only partially executing

I guess I'm a beginner at javascript and as the title suggests, my function won't fully execute.
function showBorder2(classid){
var first2 = document.getElementById("swordsmanIcon");
var second2 = document.getElementById("marksmanIcon");
var third2 = document.getElementById("scribeIcon");
first2.style.borderColor = "transparent";
second2.style.borderColor = "transparent";
third2.style.borderColor = "transparent";
classid.style.borderColor = "Aqua";
alert("1");
var classType = elementid.id;
alert("2");
window.classType = classType;
}
I've ran a little test and i have discovered that alert 1 triggers, but alert 2 does not... This is probably a simple mistake but I really can't see it.
Thanks in advance!

if alert1 is triggering but not alert2, the problem must be that elementid is not defined and trying to access a property of an undefined variable will throw an error and break execution of your js. The solution:
a) make sure to define elementid
b) if you can't guarantee definition of elementid, add a check to see if it is defined before trying to access a child property.
A simple shorthand for this is var classType = elementid && elementid.id;
^ that's short for something like this:
var classType;
if(elementid) {
classType = elementid.id;
}

Probably one of your element variable (first2, second2, third2, classid) is either null or undefined. It is good defensive programming (especially in javascript) to check for null or undefined before using the variable.
I'm guessing when the showBorder2 function is called, the parameter passes to "classid" either is not a valid element or nothing is pass to it.

why value is not changing of a `var` when it is in the scope of the function

just look at this question: What is the scope of variables in JavaScript?
in the answer which is accepted look at the point 3
according to him a will be 4 but now look at my function:
function JIO_compiler(bpo){ // bpo means that " behave property object " and from here i will now start saying behave property to behave object
var bobj = bpo, // bobj = behave object
bobj_keys = Object.keys(bobj), // bobj_keys = behave object keys. This willl return an array
Jcc_keys = Object.keys(JIO_compiler_components), // Jcc = JIO compiler components
function_code = ""; // get every thing written on every index
if (bobj.hasOwnProperty('target') === false) { // see if there is no target defined
console.log("No target is found"); // tell if there is no target property
throw("there is no target set on which JIO-ASC will act"); // throw an error
};
if (bobj.hasOwnProperty('target') === true) {
console.log("target has been set on "+ bobj['target']+" element"); //tell if the JIO-ASC has got target
function x(){
var target_ = document.getElementById(bobj['target']);
if (target_ === null) {throw('defined target should be ID of some element');};
function_code = "var target="+target_+";";
console.log("target has successfully been translated to javascript");//tell if done
};
};
for(var i = 0; i < bobj_keys.length; i++){
if(bobj_keys[i] === "$alert"){ // find if there is $alert on any index
var strToDisplay = bobj[bobj_keys[i]];
var _alert = JIO_compiler_components.$alert(strToDisplay);
function_code = function_code+ _alert;
};
};// end of main for loop
alert(function_code);
new Function(function_code)();
};
well it is big... but my problem is in the second if statement. now according to the accepted answer the value of function_code should change according to what is instructed. but when at last i alert the function code then it alert blank. i mean it should alert at least var target = something ; and the last console.log statement of this if statement is not showing text in the console.
so what is wrong in this ?

You're setting function_code inside the definition for function x(), but x() is never called. function_call won't change until you make a call to x.

thats because your variable is inside the function scope, you need to define your variable outside of it, as
function_code = "";
function JIO_compiler(bpo){
....
};// end of main for loop
//call the function
JIO_compiler(some_parameter);
//alert the variable
alert(function_code);
you need to call the function JIO_compiler() first so that the appropriate value is set to function_code variable from JIO_compiler() function, as

How to override console.log

I am using the following code to override the console.log function, because I want to print console.log only if showConsole returns true.
var proxyConsolelog = window.console.log;
console.log=function(msg){
try{
if(Boolean(showConsole))
{
proxyConsolelog(msg);
}
}catch(e){
alert(JSON.stringify(e.message));
proxyConsolelog('ERROR-->>'+e.message);
}
}
The proxyConsolelog line creates a problem, and alert(JSON.stringify(e.message)); is giving me a "Type error".
And I get this:
void SendDelegateMessage(NSInvocation *): delegate
(webView:runJavaScriptAlertPanelWithMessage:initiatedByFrame:) failed
to return after waiting 10 seconds. main run loop mode:
kCFRunLoopDefaultMode
in the log.
How can I achieve this?

The problem you have is that the receiver (this) when you call your function, isn't the console.
You can do this :
var proxyConsolelog = window.console.log.bind(window.console);
If you need to be compatible with IE8 (which doesn't have bind), you may do this :
var logFun = window.console.log;
var proxyConsolelog = function(){
logFun.apply(window.console, arguments)
};
As you tagged the question jquery, then you may also use proxy :
var proxyConsolelog = $.proxy(window.console.log, window.console);
Once you have your new function, you can call it just like console.log :
proxyConsolelog('some', {arg:'uments'});

Develop Reference

JavaScript is the programming language of the Web.

Variable cannot be changed inside Window object - javascript

Try changing the for loop to this: for (var i = 0; i < data.messages.length; i++){ var dataMsg = data.messages[i].msg; output = dataMsg; alert(output); //*1 } I don't know if there is an issue with assigning msg.msg to output.

Related

Continue executing a dom command

How to dynamically change the contents of a function using JavaScript

Function only partially executing

why value is not changing of a `var` when it is in the scope of the function

How to override console.log

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