Best way to solve this "ReferenceError: Function is not defined"? - javascript

I have an AEM page with multiple components, these components have a .js file with a function that encloses all the client side logic. We then call that function inside the component's HTML:
<script>
window.bootstrap_component(function() {
init_component_name();
});
</script>
As stated before init_component_name is the name of a function that encompasses all the logic we need:
function init_component_name() {
//DO STUFF
}
The wrapper bootstrap_component fuction is defined in the shared head.html of all our pages as:
<script>
window.bootstrap_component = function (handler) {
if (typeof handler === 'function') {
if (document.readyState === "complete" || document.readyState === "loaded" || document.readyState === "interactive") {
handler();
} else {
document.addEventListener("DOMContentLoaded", function() {
handler();
});
}
}
}
</script>
This works okay and we don't have any actual issues but we recently started using Bugsnag for error monitoring and reporting and we're getting reports for almost every component saying ReferenceError on page so/and/so init_component_name() is not defined.
The reason I think this is happening is because the init_component_name() function is not declared within the script tag and because this, function(init_component_name) has been attached to the window object it is executing fine and you don't see any console errors.
If I am correct would modifying those scripts tags to be like this work?
<script>
window.bootstrap_component(function() {
window.init_component_name();
})
</script>
A colleague of mine wants to add a timeout to the init_component_name functions of like 1ms but it rubs me the wrong way. Is there a more sensible approach?

If I am correct would modifying those scripts tags to be like this work?
window.bootstrap_component(function() {
window.init_component_name();
})
Yes, but you then have the problem that you're writing multiple data to the global namespace, window, which isn't ideal. What if another third-party script decides to override it?
Ideally you'd have a single namespace and put everything on there, and write only that namespace to window.
window.something = {};
something.bootstrap_component = { //...
and
something.init_component_name = () => {
//DO STUFF
}
Or better still, use modules (though that will need some light code refactoring).
Don't do the timeout hack. It's really, really horrible; what if scripts take longer than a second to load for some reason? You're also forcing your UI to wait a second, often unnecessarily. This hack tends to feature where chronology and scope has not been thought out properly.

Related

Defer functions until jQuery has loaded (or another fixed point)

Question: is there anything wrong with using the following method to defer running code until after jQuery has loaded (or until another fixed point)?
Bonus question: is there a better way to do it? (E.g. not having to name the functions in window.deferred, like window.deferred.afunction)
In my page (before jQuery):
<script>
window.deferred = window.deferred || {};
window.deferred.afunction = function() {
console.log('afunction is running');
};
window.deferred.anotherfunction = function() {
console.log('anotherfunction is running');
};
</script>
In my JS (after jQuery when I'm ready to execute my deferred functions):
/* Run deferred functions */
if(window.deferred && typeof window.deferred === 'object') {
for (var fn in window.deferred) {
if (typeof window.deferred[fn] == 'function') {
window.deferred[fn]();
}
}
}
Demo: https://jsfiddle.net/j4sqy5kf/4/
As far as I can tell it works fine. But I consider myself amateur at JavaScript - I can write it but don't always understand how it's working.
So far all the ways I've found to do this (e.g. http://snipplr.com/view/54863/) rely on having setTimeout or setInterval and calling a check function, which seems quite inelegant to me.
There's also Require.js, which I believe could be used, but I think it's overkill to achieve exactly what I want as it primarily serves a different purpose.
Background
I'm writing a post for my blog in Markdown, and I'm writing a little JavaScript inside the page to manage some hidden content. I want to use jQuery in my script, but jQuery is loaded in the footer - so, I want an elegant way to defer execution of my inline script until after jQuery has loaded.
I have jQuery in my footer and a general.js script, in which most of the rest of my JavaScript runs. I'd like to run the 'In my page' bits inside each blog post, and leave the 'In my JS' bit in general.js so I never have to worry about it again.
I know I could define but not execute the functions, but I don't want to have to update general.js each time (e.g. add function1(), function2(), etc.)
I want it to automatically loop through all deferred functions.
I don't really see anything wrong with doing it this way. I would however use an array instead of an object:
/* Run deferred functions */
if(window.deferred && Array.isArray(window.deferred)) {
window.deferred.forEach(function (fn) {
if (typeof fn === 'function') {
fn();
}
});
}
.hello-world {
color: #f00;
font-size: 3em;
font-family: verdana;
}
.jq {
color: #00f;
}
<script>
window.deferred = window.deferred || [];
window.deferred.push(function aFunction() {
console.log('aFunction is running');
});
window.deferred.push(function anotherfunction () {
console.log('anotherfunction is running');
});
window.deferred.push(function doSomethingWithJquery () {
jQuery('<div class="hello-world">Hello from <span class="jq">jQuery</span>!</div>').appendTo('body');
});
</script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
If you ever are looping over an object with for...in like your original code does, you should use hasOwnProperty to check that the object actually contains that property and you are not getting a property from the prototype chain.
An easier way of achieving what you want is by using DOMContentLoaded.
<script>
window.addEventListener('DOMContentLoaded', function() {
$( document ).ready(function() {
console.log('my other scripts including jquery has loaded now');
});
});
</script>
But I would stop and think about the reason for preferring inline scripts instead of your general.js, as inline scripts has a negative impact on performance, and prevents caching. If it is code separation you're after, you can achieve it by other means, depending on your setup.

<script> dynamic script load issue - weird behaviour

I am having a weird issue that is rather difficult to recreate, but I will try to explain to the best of my abilities.
I have a setup.js which is a file that includes parameters for the scripts to be added to the document by the main script, like so:
{
script1: true,
script2: true,
script3: false
}
I have a main script file, lets call it main.js which basically checks the setup file and then for every "true" does the following:
var element = document.createElement('script');
element.src = "path/to/file.js"
document.getElementsByTagName('body').appendChild(element);
Now I've checked using console.log, and the main.js file is the one that has to execute all the way to the end until any of the files added to the body begin loading, however they are then loaded one-by-one and should become ready for usage.
Now here comes the tricky part
I need to know when ALL of them are finished loading in order to be able to use their functions in the rest of the main.js file, so I need some sort of "onload" handler. I've tried to attach a addEventListener('load', function(){}) to the last element that was added, and it worked.
However.....
Once I changed the event listener function to something such as:
addEventListener('load' function(){
script1Function(); //Which is defined in script1
script2Function(); //Which is defined in script2
}
It started throwing errors such as "script1Function is not defined".
I know that both scripts are loaded at this point, because I did a console.log("I have loaded") as the last line of each script, and those appeared in the console, but it is not possible to use the function definitions that were defined in these files.
What is even more.... if I instead do the following event handler:
addEventListener('load' function(){
alert("Last script loaded"); //This line was ADDED
script1Function(); //Which is defined in script1
script2Function(); //Which is defined in script2
}
It all suddenly works.
Adding "alert("whatever");" allows me to use the functions defined in the files.... I would assume it has something to do with "time needed for me to click "OK" on the alert dialog... but the entire thing doesn't make sense, because I know functions are defined by the time I am calling them.
/*
Example usage:
importAsync(["script1.js", "script2.js", "script3.js"]);
waitUntil(function() {
return ((typeof(script1Function) !== "undefined")
&& (typeof(script2Function) !== "undefined")
&& (typeof(script3Function) !== "undefined"));
});
*/
function waitUntil(testFunc) {
var start = Date.now();
var timeout = 3000;
do {
if((Date.now() - start) > timeout) {
console.log("waitUntil() timed out");
return false;
}
} while(!testFunc());
}
This is what I meant in the comments.
I direct your attention to the example above the function:
importAsync(["script1.js", "script2.js", "script3.js"]);
waitUntil(function() {
return ((typeof(script1Function) !== "undefined")
&& (typeof(script2Function) !== "undefined")
&& (typeof(script3Function) !== "undefined"));
});
importAsync is whatever function/method you have for loading the .js files - it's not relevant.
What is relevant, is waitUntil and the function you pass it. In the example above, I check whether functions from all three scripts exist (ergo: are not equal to undefined) and only then will execution of the script continue, due to the nature of the do..while loop. As I also mentioned in the comments, you're going to want a timeout on the do..while loop to prevent an infinite loop. You could add a parameter to waitUntil for the timeout as well if you'd like.
I hope this gives you a basic idea of what I meant in the comments and if you have any further questions, fire away!

See whether object is undefined before executing script

I'm currently loading a custom.js file on my site and it calls various functions. However, to keep the size down I only load the libraries needed on certain pages.
Because of this, since the custom.js file is loaded on every page and it calls functions that the particular page may not have, I get undefined is not a function errors on my site on certain pages.
What I would like to be able to do is determine if something is defined before executing the code to keep the errors from popping up.
For an example, I'm using Jarallax (http://www.jarallax.com/) on my front page only with the following:
var jarallax = new Jarallax();
jarallax.addAnimation('div#bigSlider',[{progress:'0%',marginTop:'0px'},{progress:'100%', marginTop:'-200px'}]);
Since Jarallax is only loaded on the homepage and no others I get the undefined function error on all pages but the hompeage. How could I first confirm Jarallax is loaded before attempting to execute the code?
Since referring to undefined variables raises a ReferenceError exception, you could use a try/catch block to handle the exception.
try {
var jarallax = new Jarallax();
}
catch (e) {
// desired behavior for this situation.
}
More on try/catch blocks.
However, to keep the size down I only load the libraries needed on
certain pages. Because of this I get "undefined is not a function"
errors on my site on certain pages.
So this means you're not doing it properly on every page?
You could solve this by using a wrapper object or class:
(function($){
var wrapper = {
init: function(){
var jarallax;
if (typeof Jarallax == 'function'){
jarallax = new Jarallax();
jarallax.addAnimation('div#bigSlider',[{progress:'0%',marginTop:'0px'},{progress:'100%', marginTop:'-200px'}]);
}
}
};
// once the DOM is read
$(function(){
wrapper.init();
});
}(window.jQuery));
By stalling the init function on the DOM ready, you can be certain the script is loaded if you make sure the script tag for Jarallax is added before the wrapper in the HTML. In any other case the init function won't do a thing.
if (typeof jarallax === "undefined") {
var jarallax = {
obj: {},
return {
obj;
};

How can I force JavaScript to wait until after a dynamically added script file has completed loading?

I'm trying to write a function which will append a javascript file to the DOM, but I am looking to have the rest of the code wait until the newly added JS file is completely loaded. Here is an example of what I am trying to accomplish, although this code doesn't work properly:
$(document).ready(function () {
var newScript = document.createElement("script");
newScript.setAttribute("type", "text/javascript");
newScript.src = "http://www.domain.com/script.js";
document.getElementsByTagName("body")[0].appendChild(newScript);
$(newScript).ready(function () { // This is the idea of what I'm trying to do, but this doesn't seem to actually wait until the new file is completely loaded.
foo.bar(); // foo is a new global variable which is declared in the newScript. This causes an error "foo is not defined".
// Here is where more code I wish to execute should continue.
});
});
As Musa mentioned in the comments above. Use jQuery's getScript and use the success callback function to trigger your other functions.
If you want more robust module loading functionality, then require.js works great in this capacity. Check out: http://requirejs.org/docs/why.html for an overview. I use require.js specifically for lazy-loading script modules.
Using jQuery (as you've tagged), it's extremely easy:
$.getScript('/script.js', function() {
foo.bar();
});
There's a few different ways to do this... via libraries or "by hand," so to speak, using only the browser APIs and straight JavaScript. For an answer on how to do this in JS only, look here for Stoyan's post to give you guidance. Basically, the gist of it is setting an event handler to both the script's unload and onreadystatechange properties and then check to see if the readyState is "loaded" or "complete" (if it exists at all). It would look something like this:
var done = false;
newScript.onload = newScript.onreadystatechange = function () {
if (!done && (!newScript.readyState || newScript.readyState === "loaded" || newScript.readyState === "complete)) {
done = true;
// run your actual code here
}
};

Javascript Execute After Page Render IE6

I am having trouble with some JavaScript running before the page is completely rendered in IE 6 (maybe other versions too but just testing IE6 for now. Firefox seems to be OK). I can get around this by calling the js on window.onload like this:
window.onload = function(){doIt();}
However, my concern is the fact that I will overwrite anything else that may already be in window.onload. The code will be used as part of a library so I can not guarantee that window.onload will not be set somewhere else by someone else. I would rather append my function to the onload event like this:
window.onload += function(){doIt1();}
window.onload += function(){doIt2();}
But when I do so, only doit2() is called. Is there a way to register an event handler for when the page is fully rendered? My second thought would be to just put my code in a loop checking to make sure all my objects exist before running. But I am scared that this could potentially lockup the browser.
Just for some background info, my code is hiding/showing iFrames. I know that I can use the iFrame's onload attribute but I need all of the iFrames to be fully loaded before calling the code.
Any thoughts from the community? Thanks in advance for you input.
Use this generic addLoadEvent function...
function addLoadEvent(func) {
if(typeof window.onload != 'function')
window.onload = func;
else {
var oldLoad = window.onload;
window.onload = function() {
if(oldLoad) oldLoad();
func();
}
}
}
This essentially queues up functions to be executed. It never overwrites a previously assigned handler. Sample usage below...
addLoadEvent(function() { alert("One!"); });
addLoadEvent(two);
function two() {
alert("Two!");
}
I want to mention that libraries like jQuery take care of known issues like this for you.

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