Clean way to map an array in node.js or JavaScript

Question

Let's say I have a function and an array. I want to modify the array by applying the function to each entry in the array. The function does NOT modify the value directly; it returns a new value.

In pseudo-code,

for (entry in array) {
    entry = function(entry);
}

There are a couple ways to do this that occurred to me:

for (var i = 0; i < arr.length; i++) {
    arr[i] = fn(i);
}

Or, since I am using node.js and have underscore built in:

arr = _.map(arr, fn);

But this both seem a little clunky. The standard "for" block feels overly verbose, and the _.map function re-assigns the entire array so feels inefficient.

How would you do this?

Yes, I am aware I'm overthinking this :)

Just use the underscore-function until you are certain that it is a performance issue. It is very readable and clean, so unless it is actually an issue, your "feeling of inefficiency" shouldn't stop you from moving on to more pressing issues :) — PatrikAkerstrand
– PatrikAkerstrand, Commented Mar 15, 2012 at 23:24

fent · Accepted Answer · 2012-03-15 23:37:49Z

25

The Array#map() method.

var arr = arr.map(fn);

_.map() is probably implemented in the same way.

answered Mar 15, 2012 at 23:37

fent

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1 Comment

RyanWilcox Over a year ago

If you're using Node.js you know what JS Interpreter you are using, thus you know that things from ECMAScript5 are implemented... which includes Array#map :)

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