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I am reading through some javascript code, and I have seen a lot of code that looks like this:

processMethod = processMethod || function(){};

it's usually found inside a function. I believe it's a shorthand code, but I am not sure what it does.

Does it check to see if processMethod has a value, and if it doesn't declares it as a function that can be defined later?

  • means if `processMethod` doesn't exists, just create a an empty function to prevent `processMethod -- undefined error.` – Praveen Jan 31 '14 at 04:57
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    Sorry #Raymond Chen. I had no idea how to ask the question, or even what terms to search for before posting it. –  Jan 31 '14 at 04:59
  • Yeah, the important part was punctuation, which SO doesn't know how to search for. – Raymond Chen Jan 31 '14 at 05:07
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    @RaymondChen, @gdaniel: [`[javascript] what does "||" do`](https://stackoverflow.com/search?q=[javascript]+what+does+%22||%22+do) – Felix Kling Jan 31 '14 at 05:31

2 Answers2

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In words: 

if there is no processMethod, create it empty.

|| works with booleans, so it checks if the first operand processMethod has a boolean-equivalent. If processMethod is defined and not null, the boolean-equivalent is true. If processMethod is undefined or null, the boolean-equivalent is false. In the false-case, || looks for a boolean-equivalent of the second-operand, its not null so its boolean-equivalent is true.

false || true resolves to true so processMethod becomes function(){}.

Btw function(){} is a empty function whom used to not throw a error on processMethod()

Grim
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It essentially checks whether it exists or not. If it doesn't exist, assign it.

function doSomething(o) {
    o = o || {};
}

In the above case, it checks whether a value for o was passed. If not it assigns an empty object to it.

Evan Trimboli
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