How to run a function when the page is loaded?

How to run a function when the page is loaded?

I want to run a function when the page is loaded, but I don’t want to use it in the tag.
I have a script that runs if I initialise it in the , like this:
function codeAddress() {
// code
}

But I want to run it without the and I have tried a lot of things, e.g. this:
window.onload = codeAddress;

But it is not working.
So how do I run it when the page is loaded?

Solutions/Answers:

Solution 1:

window.onload = codeAddress; should work – here’s a demo, and the full code:

<!DOCTYPE html>
<html>
    <head>
        <title>Test</title>
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
        <script type="text/javascript">
        function codeAddress() {
            alert('ok');
        }
        window.onload = codeAddress;
        </script>
    </head>
    <body>
    
    </body>
</html>

<!DOCTYPE html>
<html>
    <head>
        <title>Test</title>
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
        <script type="text/javascript">
        function codeAddress() {
            alert('ok');
        }
        
        </script>
    </head>
    <body onload="codeAddress();">
    
    </body>
</html>

Solution 2:

Rather than using jQuery or window.onload, native JavaScript has adopted some great functions since the release of jQuery. All modern browsers now have their own DOM ready function without the use of a jQuery library.

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I’d recommend this if you use native Javascript.

document.addEventListener('DOMContentLoaded', function() {
    alert("Ready!");
}, false);

Solution 3:

Taking Darin’s answer but jQuery style. (I know the user asked for javascript).

running fiddle

$(document).ready ( function(){
   alert('ok');
});​

Solution 4:

Alternate solution. I prefer this for the brevity and code simplicity.

(function () {
    alert("I am here");
})();

This is an anonymous function, where the name is not specified.
What happens here is that, the function is defined and executed together.
Add this to the beginning or end of the body, depending on if it is to be executed before loading the page or soon after all the HTML elements are loaded.

Solution 5:

window.onload = function() { … etc. is not a great answer.

This will likely work, but it will also break any other functions already hooking to that event. Or, if another function hooks into that event after yours, it will break yours.
So, you can spend lots of hours later trying to figure out why something that was working isn’t anymore.

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A more robust answer here:

if(window.attachEvent) {
    window.attachEvent('onload', yourFunctionName);
} else {
    if(window.onload) {
        var curronload = window.onload;
        var newonload = function(evt) {
            curronload(evt);
            yourFunctionName(evt);
        };
        window.onload = newonload;
    } else {
        window.onload = yourFunctionName;
    }
}

Some code I have been using, I forget where I found it to give the author credit.

function my_function() {
    // whatever code I want to run after page load
}
if (window.attachEvent) {window.attachEvent('onload', my_function);}
else if (window.addEventListener) {window.addEventListener('load', my_function, false);}
else {document.addEventListener('load', my_function, false);}

Hope this helps 🙂

Solution 6:

Take a look at the domReady script that allows setting up of multiple functions to execute when the DOM has loaded. It’s basically what the Dom ready does in many popular JavaScript libraries, but is lightweight and can be taken and added at the start of your external script file.

Example usage

// add reference to domReady script or place 
// contents of script before here

function codeAddress() {

}

domReady(codeAddress);