What is context in _.each(list, iterator, [context])?

javascript functional-programming underscore.js this
ram picture ram · Feb 9, 2011 · Viewed 160.6k times · Source

I am new to underscore.js. What is the purpose of [context] in _.each()? How should it be used?

Answer

user113716 picture user113716 · Feb 9, 2011

The context parameter just sets the value of this in the iterator function.

var someOtherArray = ["name","patrick","d","w"];

_.each([1, 2, 3], function(num) { 
    // In here, "this" refers to the same Array as "someOtherArray"

    alert( this[num] ); // num is the value from the array being iterated
                        //    so this[num] gets the item at the "num" index of
                        //    someOtherArray.
}, someOtherArray);

Working Example: http://jsfiddle.net/a6Rx4/

It uses the number from each member of the Array being iterated to get the item at that index of someOtherArray, which is represented by this since we passed it as the context parameter.

If you do not set the context, then this will refer to the window object.

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