Delay script loading

Question

So if I have the following:

and I simply want

Answer 1

I have created for ReactJS and its worked for me.

1. File: widget.js with promise:

const delayTime = 20000; // loading 20sec delay.

const loadJS = async () => {
    return await new Promise(function (resolve, reject) {
        var script = document.createElement('script');
        script.type = 'text/javascript';
        script.async = true;
        script.src = 'https://yoururl.com/js/widget.js';
        script.onload = resolve;
        script.onerror = () => {
            reject('Cannot load js')
            document.head.removeChild(script);
        }
        document.head.appendChild(script);
    }) }

function initLoadJS() {
    loadJS()
    .then(()=> console.log('testing'))
    .catch((error)=>console.error(error)) }

function delayLoadingJS() {
    setTimeout((event)=>initLoadJS(event), delayTime); 
} 
export default delayLoadingJS;

2. Calling delayLoadingJS() function on the page:

When page loading completed then after 20 sec later initLoadJS() method will trigger and it attach the 3rd party javascript file(https://yoururl.com/js/widget.js) on page.

componentDidUpdate(prevProps, prevState) {
    if (this.state.page !== prevState.page) {

      delayLoadingJS();
    }
}

Answer 2

The simplest way would be to let the script file load normally and just call a main function in it with setTimeout() like this:

<script type="text/javascript" src="offsite file I am referencing"></script>
<script type="text/javascript">
setTimeout(executeMainFunction, 5000);    // function in offsite js file
</script>

If you cannot do that for some reason, then you can delay the loading of the external script file like this:

setTimeout(function() {
    var headID = document.getElementsByTagName("head")[0];         
    var newScript = document.createElement('script');
    newScript.type = 'text/javascript';
    newScript.src = 'http://www.somedomain.com/somescript.js';
    headID.appendChild(newScript);
}, 5000);

Here's a reference article on dynamic loading of script files (and other types of resources): http://www.hunlock.com/blogs/Howto_Dynamically_Insert_Javascript_And_CSS.

Answer 3

You can use DOM manipulation to create a new script tag at runtime. Adding it into the document will load the external JS file just as if you had written it into the HTML in the first place.

var loadScript = function(sourceSrc){
    var scriptTag = document.createElement('script');
    scriptTag.src = scriptSrc;
    document.getElementsByTagName('head')[0].appendChild(scriptTag);
}

Answer 4

Mozilla Developer Network explains various approaches:

MDN Async Script Techniques

<script async src="file.js"></script>

or

var script = document.createElement('script');
script.src = "file.js";
document.body.appendChild(script);

or if your JavaScript is in a String:

var blob = new Blob([codeString]);
var script = document.createElement('script');
var url = URL.createObjectURL(blob);
script.onload = script.onerror = function() { URL.revokeObjectURL(url); };
script.src = url;
document.body.appendChild(script);

There is also good information when async is not async as well as how to get around those cases.

Answer 5

You can delay the script from loading, until the page finishes loading, using the HTML script defer attribute:

<script src="offsite file I am referencing" defer></script>

Answer 6

you are almost there.

in your settimeout callback function do the following:

var script = document.createElement('script');
script.src = "http://whatever.com/the/script.js";
document.getElementsByTagName('head')[0].appendChild(script);