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Editorial Team
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Asked: 2026-05-16T14:32:27+00:00

The more i use JavaScript the more i try to come up with efficient

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The more i use JavaScript the more i try to come up with efficient ways of loading and executing my scripts.
One method i have found to be really useful is loading javascript without blocking. 

function include_js(url) { 
    var script = document.createElement("script");
    script.type = "text/javascript";
    script.src = url;
    document.getElementsByTagName("head")[0].appendChild(script);
}

include_js('script.js');

JavaScript also has a window method that executes when the page has loaded.

window.onload = function() {
 alert('Script executed onload');
};

What i want to know is, how does the browser treat script executed by the window.onload method, is it blocking or non-blocking script?

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1 Answer

  1. Editorial Team

    What i want to know is, how does the
    browser treat script executed by the
    window.onload method, is it blocking
    or non-blocking script?

    Are you referring to how the code in the event handler is executed? It runs asynchronously, but since JavaScript only has one thread, it is blocks, and will be blocked itself until the thread is available.

    See this article about how timers work to get a better idea of how asynchronous methods behave in single thread environment.

    The only way to have JavaScript code that executes in parallel to other JavaScript code is to use web workers, which actually use a separate thread.

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