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POConfusion about window.onload in javascript
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copied!<p>I have one paragraph of javascript code. And i don't understand it very well. Can you expain it line by line for me? Thanks a lot. </p> <pre><code> function addLoadEvent(func) { var oldonload = window.onload; if (typeof window.onload != 'function') { window.onload = func; } else { window.onload = function() { oldonload(); func(); } } } </code></pre> <p>And here is what i'm thinking: </p> <pre><code> function addLoadEvent(func) { //define a function with a parameter 'func' var oldonload = window.onload; //assign window.onload event to variable oldonload if (typeof window.onload != 'function') { //if window.onload is not a function, then... window.onload = func; //assign 'func' to window.onload event. what does func mean? } else { //if window.onlad is a function window.onload = function() { //don't understand oldonload(); //call function oldonload() func(); //call function func() } } } </code></pre> <p>Confusions: </p> <p>window.onload is already an event, and why do we use typeof?</p> <p>function addLoadEvent(func) , window.onload = func, func(). What's the difference among these funcs? </p> <p>I'm sorry for posting a novice problem. But thanks to anyone who gives me some guidance?</p> <p>Edit:</p> <p>This is improved original code by Simon Willison. </p> <pre><code>function addLoadEvent(func) { var oldonload = window.onload; if (typeof window.onload != 'function') { window.onload = func; } else { window.onload = function() { if (oldonload) { oldonload(); } func(); } } } </code></pre>

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