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Oreilly Head First JavaScript Programming ¹

How to use an anonymous function

So, we’re creating a function to handle the load event, but we know it’s a "one time" function because the load event only happens once per page load. We can also observe that the window.onload property is being assigned a function reference—namely, the function reference in handler. But because handler is a one time function, that name is a bit of a waste, because all we do is assign the reference in it to the window.onload property.

Anonymous functions give us a way to clean up this code. An anonymous function is just a function expression without a name that’s used where we’d normally use a function reference. But to make the connection, it helps to see how we use a function expression in code in an anonymous way:

First remove the handler variable so this becomes a function expression.

function handler() { 
    alert("Yeah, that page loaded!"); 
}

window.onload = handler;

Then assign the function expression directly to the window.onload property.

window.onload = function() { 
    alert("Yeah, that page loaded!"); 
};

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