I want to transform an object like this:
[
{ name: 'john', surname: 'doe' },
{ name: 'jane', surname: 'dee' },
]
Into an array, like this. By choosing an arbitrary key (e.g: 'name')
[ 'john', 'jane' ]
What is the fastest way to achieve this? Thanks in advance.
Try use map function like this
[
{ name: 'john', surname: 'doe' },
{ name: 'jane', surname: 'dee' },
].map(function(a){return a.name;})
Array#map is an ES5 thing, but that's fine, this is NodeJS. (In client-side stuff, older browsers would need a shim.)If you don't need retro compatibility (and I think you're not going to need it, since you're on NodeJS), you can simply use:
var obj = [
{ name: 'john', surname: 'doe' },
{ name: 'jane', surname: 'dee' },
],
names = obj.map(function(item) {return item.name;});
Or, the "slowest" way:
var names = []; //obj defined before
for(var i = 0; i < obj.length; i++)
names.push(obj[i].name);
Array.prototype.map is generally slower than a simple for loop. The native map function just does more error checking internally and has the overhead of an additional function invocation for every iteration: jsperf.com/array-map-test
If you are using UnderscoreJS, you can simply write:
names = _.pluck(obj, 'name');
