Ways to determine if a dynamically generated script tag has been successfully executed

Question

Ways to determine if a dynamically generated script tag has been successfully executed

Recently, I've been experimenting with dynamically creating a script tag:

var head = document.getElementsByTagName('head')[0];
var script = document.createElement('script');
script.type = 'text/javascript';
script.charset = 'utf-8';
script.defer = true;
script.async = true;
script.text = 'insert javascript content here';
head.appendChild(script);

script.onload = function () {
    // This doesn't seem to trigger... 
    debugger;
}

Is there a way to receive notification when the script is executed within another code block? Perhaps using an event of some sort?

javascript createelement script-tag

Answer 1

Answer №1

To make this function properly, I added an ID to the script and then used JavaScript to manually trigger the load event on that specific DOM element. This method was tested only in Chrome and may encounter issues in older versions of IE as mentioned in MDN.

var head = document.getElementsByTagName('head')[0];
var script = document.createElement('script');
script.type = 'text/javascript';
script.charset = 'utf-8';
script.id = 'testing';
script.defer = true;
script.async = true;
script.onload = function () {
    console.log('The script is loaded');
}
script.text = ["console.log('This is from the script');",
               "var script = document.getElementById('testing');",
               "var event = new UIEvent('load');",
               "script.dispatchEvent(event);"].join('');
head.appendChild(script);

Check out the Fiddle

Answer 2

To make this function properly, I added an ID to the script and then used JavaScript to manually trigger the load event on that specific DOM element. This method was tested only in Chrome and may encounter issues in older versions of IE as mentioned in MDN.

var head = document.getElementsByTagName('head')[0];
var script = document.createElement('script');
script.type = 'text/javascript';
script.charset = 'utf-8';
script.id = 'testing';
script.defer = true;
script.async = true;
script.onload = function () {
    console.log('The script is loaded');
}
script.text = ["console.log('This is from the script');",
               "var script = document.getElementById('testing');",
               "var event = new UIEvent('load');",
               "script.dispatchEvent(event);"].join('');
head.appendChild(script);

Check out the Fiddle

Answer 3

Answer №2

To detect changes in an element like the head, modern browsers allow you to use a Mutation Observer. Here is an example:

observer = new MutationObserver(function (m) {
    // This function will be triggered
});
observer.observe(document.head, {childList: true});

Unfortunately, this method does not work in Internet Explorer versions lower than 11. However, you can use the onload event for IE.

Check out the live demo on jsFiddle.

Answer 4

To detect changes in an element like the head, modern browsers allow you to use a Mutation Observer. Here is an example:

observer = new MutationObserver(function (m) {
    // This function will be triggered
});
observer.observe(document.head, {childList: true});

Unfortunately, this method does not work in Internet Explorer versions lower than 11. However, you can use the onload event for IE.

Check out the live demo on jsFiddle.

Answer 5

Answer №3

Every 100 milliseconds, the code checks if the script has been appended to the DOM. This function can be utilized throughout your application without requiring event listeners or dispatch events. Additionally, you can specify a time interval within which an error will be triggered if the script fails to append.

const waitForScriptToLoad = (scriptName, checkTimeMs, timeOutMs) => {
  let elapsedTime = 0;
  return new Promise((resolve, reject) => {
    setTimeout(x => reject('script: ' + scriptName + ' Timed out!')
      , timeOutMs)
    const time = setInterval(() => {
      elapsedTime += checkTimeMs;
      if (document.body.innerHTML.indexOf(scriptName) > -1) {
        resolve(
          {
            response: 'script: ' + scriptName + ' found!',
            time: (elapsedTime / 1000).toFixed(2) + 's'
          });
        clearInterval(time);
      }
    }, checkTimeMs)
  })
}

waitForScriptToLoad('example_script.js', 100, 20000)
  .then(res => console.log(res))
  .catch(err => console.log(err))

Answer 6

Every 100 milliseconds, the code checks if the script has been appended to the DOM. This function can be utilized throughout your application without requiring event listeners or dispatch events. Additionally, you can specify a time interval within which an error will be triggered if the script fails to append.

const waitForScriptToLoad = (scriptName, checkTimeMs, timeOutMs) => {
  let elapsedTime = 0;
  return new Promise((resolve, reject) => {
    setTimeout(x => reject('script: ' + scriptName + ' Timed out!')
      , timeOutMs)
    const time = setInterval(() => {
      elapsedTime += checkTimeMs;
      if (document.body.innerHTML.indexOf(scriptName) > -1) {
        resolve(
          {
            response: 'script: ' + scriptName + ' found!',
            time: (elapsedTime / 1000).toFixed(2) + 's'
          });
        clearInterval(time);
      }
    }, checkTimeMs)
  })
}

waitForScriptToLoad('example_script.js', 100, 20000)
  .then(res => console.log(res))
  .catch(err => console.log(err))

Answer 7

Answer №4

After some research, I discovered a simple solution:

var script = document.createElement("script");

script.innerHTML = "console.log('(1) hello from inline script');"

document.head.appendChild(script);

setTimeout(
  function() {
    console.log("(2) we're done!");
  },
  0 // 👈 zero timeout
);

Explanation: Using a zero timeout essentially means "next event cycle." Since it's an inline <script> node with no network delay when appended to <head>, the browser will execute the script immediately in the next event cycle.

Avoid using the load event for this technique to work effectively.

This method has been tested successfully on IE 10 + 11, as well as the latest versions of Chrome, Firefox, Edge, Opera, and Safari.

JsFiddle

If you need your script to accommodate both inline and external scripts, check for the existence of script.src and conditionally use a load event listener or the zero timeout based on that condition.

Answer 8

After some research, I discovered a simple solution:

var script = document.createElement("script");

script.innerHTML = "console.log('(1) hello from inline script');"

document.head.appendChild(script);

setTimeout(
  function() {
    console.log("(2) we're done!");
  },
  0 // 👈 zero timeout
);

Explanation: Using a zero timeout essentially means "next event cycle." Since it's an inline <script> node with no network delay when appended to <head>, the browser will execute the script immediately in the next event cycle.

Avoid using the load event for this technique to work effectively.

This method has been tested successfully on IE 10 + 11, as well as the latest versions of Chrome, Firefox, Edge, Opera, and Safari.

JsFiddle

If you need your script to accommodate both inline and external scripts, check for the existence of script.src and conditionally use a load event listener or the zero timeout based on that condition.

Answer 9

Answer №5

Move the code to a separate .js file.

Include script.src = 'yourjs.js'; in your Script tag.

The code in the .js file will be immediately executed once the script is loaded onto the DOM.

Add an

if (console) { console.debug('Hello World.'); }

at the beginning of your yourjs.js file to view the message.

Answer 10

Move the code to a separate .js file.

Include script.src = 'yourjs.js'; in your Script tag.

The code in the .js file will be immediately executed once the script is loaded onto the DOM.

Add an

if (console) { console.debug('Hello World.'); }

at the beginning of your yourjs.js file to view the message.

Answer 11

Answer №6

Prioritize defining the onload function before setting the script source. Keep in mind that when writing Javascript using the text property, the onload event may not trigger as expected. It is recommended to utilize an external JS file and load it through the src attribute.

The correct sequence of actions should be:

Append the script element to the DOM

Define the onload function

Set the src

var head = document.getElementsByTagName('head')[0];
var script = document.createElement('script');
script.type = 'text/javascript';
script.charset = 'utf-8';
script.defer = true;
script.async = true;
head.appendChild(script);
script.onload = function () {
    // Ensuring this section works correctly
    debugger;
}
script.src = 'fileName.js';

By following this structure, your onload event will activate, allowing you to include a

console.log("script has loaded!");

statement within the function.

Answer 12

Prioritize defining the onload function before setting the script source. Keep in mind that when writing Javascript using the text property, the onload event may not trigger as expected. It is recommended to utilize an external JS file and load it through the src attribute.

The correct sequence of actions should be:

Append the script element to the DOM

Define the onload function

Set the src

var head = document.getElementsByTagName('head')[0];
var script = document.createElement('script');
script.type = 'text/javascript';
script.charset = 'utf-8';
script.defer = true;
script.async = true;
head.appendChild(script);
script.onload = function () {
    // Ensuring this section works correctly
    debugger;
}
script.src = 'fileName.js';

By following this structure, your onload event will activate, allowing you to include a

console.log("script has loaded!");

statement within the function.

Answer 13

Answer №7

If you're looking to test things out, consider using the alert() function as a quick way to check for functionality. However, upon review of your code, it seems that there might be an issue with how the function is being called. It's possible that the "onload" event handler should be included in the dynamic creation section prior to appending the element.

A while back, I wrote some code to handle dynamic script creation, which has been successful. My approach involves two primary functions: one for creating scripts by loading data from ".js" files and another for executing those functions sequentially based on their names (using the "eval()" function). Notably, your function lacks a distinct name, which could complicate matters. While using eval() can raise concerns, it should be safe as long as you are only invoking code that you have authored entirely.

The provided code empowers the browser, rather than the web server, to generate a menu featuring clickable link items dynamically. Each link may resemble a standard hyperlink but operates as a JavaScript construct, necessitating enabled JavaScript support for interaction — though this requirement aligns with the initial setup of the menu:

 // Code snippet for initializing menu generation
 var F00, F01, F02, F03, F04, F05, F06, F07, F08, F09,
     F10, F11, F12, F13, F14, F15, F16, F17, F18, F19;
 var dat = new Array();
 var form, script, str, st2, tmp, tmp2, dtno, indx, unde;

 function initialize()
 { window.name="MyMenu";
   form = document.getElementById('MENU');
   for(indx=0; indx<20; indx++)
   {
     str = "0" + indx;
     tmp = str.length - 2;
     str = str.substr(tmp);
     script = document.createElement('script');
     script.type = 'text/javascript';
     script.src = str + ".js";
     form.appendChild(script);
   }
   window.setTimeout("BuildMenu();", 1000); 
   return;
 }

... Continues with further instructions for building the menu and relevant HTML integration ...

Note: The provided code accommodates up to 20 menu items, even if fewer are currently available. It gracefully handles scenarios where certain ".js" files among the maximum set do not exist.

Answer 14

If you're looking to test things out, consider using the alert() function as a quick way to check for functionality. However, upon review of your code, it seems that there might be an issue with how the function is being called. It's possible that the "onload" event handler should be included in the dynamic creation section prior to appending the element.

A while back, I wrote some code to handle dynamic script creation, which has been successful. My approach involves two primary functions: one for creating scripts by loading data from ".js" files and another for executing those functions sequentially based on their names (using the "eval()" function). Notably, your function lacks a distinct name, which could complicate matters. While using eval() can raise concerns, it should be safe as long as you are only invoking code that you have authored entirely.

The provided code empowers the browser, rather than the web server, to generate a menu featuring clickable link items dynamically. Each link may resemble a standard hyperlink but operates as a JavaScript construct, necessitating enabled JavaScript support for interaction — though this requirement aligns with the initial setup of the menu:

 // Code snippet for initializing menu generation
 var F00, F01, F02, F03, F04, F05, F06, F07, F08, F09,
     F10, F11, F12, F13, F14, F15, F16, F17, F18, F19;
 var dat = new Array();
 var form, script, str, st2, tmp, tmp2, dtno, indx, unde;

 function initialize()
 { window.name="MyMenu";
   form = document.getElementById('MENU');
   for(indx=0; indx<20; indx++)
   {
     str = "0" + indx;
     tmp = str.length - 2;
     str = str.substr(tmp);
     script = document.createElement('script');
     script.type = 'text/javascript';
     script.src = str + ".js";
     form.appendChild(script);
   }
   window.setTimeout("BuildMenu();", 1000); 
   return;
 }

... Continues with further instructions for building the menu and relevant HTML integration ...

Note: The provided code accommodates up to 20 menu items, even if fewer are currently available. It gracefully handles scenarios where certain ".js" files among the maximum set do not exist.

Ways to determine if a dynamically generated script tag has been successfully executed

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

Answer №7

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