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My question is about the map method of arrays in JavaScript.
You can pass it a function that takes a second argument, the index of the current element of the array being processed, but... to what purpose? What happens when you do it and what's the difference when you don't?
What would you use this feature for?
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In JavaScript, array is a single variable that is used to store different elements. It is often used when we want to store list of elements and access them by a single variable.
An array can be created using array literal or Array constructor syntax. Array literal syntax: var stringArray = ["one", "two", "three"]; Array constructor syntax: var numericArray = new Array(3); A single array can store values of different data types.
The index of the current item is always passed to the callback function, the only difference if you don't declare it in the function is that you can't access it by name.
Example:
[1,2,3].map(function(o, i){ console.log(i); return 0; }); [1,2,3].map(function(o){ console.log(arguments[1]); // it's still there return 0; }); Output:
0 1 2 0 1 2 Demo: http://jsfiddle.net/Guffa/k4x5vfzj/
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