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What does “options = options || {}” mean in Javascript?
What does the following line of Javascript code do?
var somevar = window.somevar || {};
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It sets somevar to window.somevar if window.somevar exists and is not boolean false, otherwise it sets it to an empty object {}
It's a common idiom for handling variables which may not have been set.
Rob Agar
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Similar to a coalesce it seems – Joe Phillips Apr 01 '11 at 03:54
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I was 'bout to go all ASCII art on this question, but English seems to be a better solution. – Blender Apr 01 '11 at 03:55
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so by setting it to an empty object, does that in turn become available as window.somevar? – VinnyD Apr 01 '11 at 03:55
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@VinnyD yes, if the context ('this') is the window, which is true for simple scripts running in a page – Rob Agar Apr 01 '11 at 04:02
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It's an either/or assignment. If window.somevar is false or undefined, then somevar is set equal to {}. Otherwise it's set equal to window.somevar.
dgilland
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This will evaluate the expression window.somevar as a boolean expression. If it evaluates to true then it will return the value of window.somevar. If it evaluates to false then it will return the empty object {}
JaredPar
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@Ketan experiments indicate it's set to the value. Though I'm not 100% sure on this point – JaredPar Apr 01 '11 at 04:03
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My experiment suggests it's set to the reference. http://jsfiddle.net/ft8d2/2/ Edit:@dgilland is right – Ketan Apr 01 '11 at 04:06
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1It depends on what `window.somevar` is. If it's an object, then `somevar` will point to the same object that `window.somevar` points. So if you then modify a property of `window.somevar`, it will modify the corresponding property of `somevar`. – dgilland Apr 01 '11 at 04:06
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1@Ketan that's because in your scenario you created and modified an object. For simple values it uses the value (http://jsfiddle.net/RpvUp/). – JaredPar Apr 01 '11 at 04:07