Add event handler for body.onload by javascript within <body> part

We want to include a maps from Google Maps API in our document. The documentation tells to initialize the map with a function called by the onload() event of the body.

The ordinary way to call:

<body onload="initialize_map();">

This doesn't work out for us because we're using Template::Toolkit and the <body> tag is already included in our wrapper. In short: The <body> tag is already printed when our javascript code starts running.

I tried something like this but it does only work for onclick, not onload. I guess that's because the javascript code is beneath the <body> tag itself.

var body = document.getElementsByTagName("body")[0];

body.addEventListener("load", init(), false);

function init() {
        alert("it works!");
};

Any help how to fire up a Google Maps map appreciated!

Answers:

Answer
body.addEventListener("load", init(), false);

That init() is saying run this function now and assign whatever it returns to the load event.

What you want is to assign the reference to the function, not the result. So you need to drop the ().

body.addEventListener("load", init, false);

Also you should be using window.onload and not body.onload

addEventListener is supported in most browsers except IE 8.

Answer

You should really use the following instead (works in all newer browsers):

window.addEventListener('DOMContentLoaded', init, false);
Answer

As @epascarello mentioned for W3C standard browsers, you should use:

body.addEventListener("load", init, false);

However, if you want it to work on IE<9 as well you can use:

var prefix = window.addEventListener ? "" : "on";
var eventName = window.addEventListener ? "addEventListener" : "attachEvent";
document.body[eventName](prefix + "load", init, false);

Or if you want it in a single line:

document.body[window.addEventListener ? 'addEventListener' : 'attachEvent'](
    window.addEventListener ? "load" : "onload", init, false);

Note: here I get a straight reference to the body element via the document, saving the need for the first line.

Also, if you're using jQuery, and you want to use the DOM ready event rather than when the body loads, the answer can be even shorter...

$(init);
Answer

As we were already using jQuery for a graphical eye-candy feature we ended up using this. A code like

$(document).ready(function() {
    // any code goes here
    init();
});

did everything we wanted and cares about browser incompatibilities at its own.

Answer

Simply wrap the code you want to execute into the onload event of the window object:

window.onload = function(){ 
   // your code here
}

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