Loading Javascript Dynamically and how to check if the script exists

Question

I am using the following technique to load up Javascript dynamically:

var script = document.createElement(\"script\");
script.type = \"text/javascript\";
scr         


        

Answer 1

Recently in my vue.js project I tried to something like this, I am using es6 so make sure you have the setup. This is just vanilla javascript, so this should run without any issue.

function handleLoad() {
  // on scirpt loaded logic goes here
  ...
};

function handleLoadError(yourScript) {
  // on scirpt loading error logic goes here
  ...

  // remove the script element from DOM if it has some error
  document.head.removeChild(yourScript);
};

function generatePan(token) {
  // if script does not exist only then append script to DOM
  if (!document.getElementById('your-script')) {
    const yourScript = document.createElement('script');
    yourScript.setAttribute('src', 'https://your-script.js');
    yourScript.setAttribute('id', 'your-script');
    yourScript.async = true;
    yourScript.addEventListener('load', () => handleLoad(), false);
    yourScript.addEventListener('error', () => handleLoadError(yourScript), false);

    document.head.appendChild(yourScript);
  } else {
    // runs if script is already loaded DOM
    handleLoad();
  }
};

Also, please check this link, even this may help.

Answer 2

Listening for events on script elements is not considered reliable (Source). One option that comes to mind is to use setTimeout() to poll for a variable that you expect to be defined in your external script. After x seconds, you could timeout your poll and consider the script as broken.

External Script: file.js:

var MyLibrary = { };

Main document:

var poll;
var timeout = 100; // 10 seconds timeout
var script = document.createElement('script');
script.type = 'text/javascript';
script.src = 'file.js';
document.body.appendChild(script);

poll = function () {
  setTimeout(function () {
    timeout--;
    if (typeof MyLibrary !== 'undefined') {
      // External file loaded
    }
    else if (timeout > 0) {
      poll();
    }
    else {
      // External library failed to load
    }
  }, 100);
};

poll();

Answer 3

var script = document.createElement("script");
script.type = "text/javascript";
script.src = "file.js";

You need to add a callback for this script.

1st: Create the call back:

function callbackFn(callbackArgs) = {
       console.log("script is loaded with the arguments below");
       console.log(callbackArgs);
    }

2nd: Add an event listener to the script. Both Firefox and Chrome support onload event so you can use it like this:

script.onload = callbackFn();

For IE... You can add an event listener for a state change like this:

script.onreadystatechange = function() {
    if ( this.readyState != "loaded" ) return;
    callbackFn();
    }

Last: Append the script to the body like you used to do.

document.body.appendChild(script);

For further information, please refer to this acticle.