Performance of modifying an array in an object: to use a variable, or not?

Question

Consider the following JavaScript global object:

var obj = { key1: [ 'data1', 'data2', ... ], key2: [ 'data1, 'data2', ... ], ... }

Assume I have a function that needs to modify the array assigned to a specific key in obj. Is it more efficient to use a local variable for my computations and modify the array at the end of my function, or should I be modifying the array directly, since it's not deep within the object?

In essence, I am asking which function is more efficient:

function local_variable() {
    var foo = [];
    $( selector ).map(function() {
        foo.push( $( this ).val() );
    });
    obj[ keyx ] = foo;
}

versus

function global_object() {
    obj[ keyx ] = [];
    $( selector ).map(function() {
        obj[ keyx ].push( $( this ).val() );
    });
}

As always, if there is an even better way to do what these functions do, please enlighten me.

While both of the functions "work", it's an inappropriate use of the .map function. Maybe this helps to understand it better: en.wikipedia.org/wiki/Map_function. — Felix Kling
– Felix Kling, Commented Jun 15, 2013 at 20:01
The question is moot. You are using the map method wrong. It's used to loop one array and return another, but you are using it as the each method. — Guffa
– Guffa, Commented Jun 15, 2013 at 20:01

adeneo · Accepted Answer · 2013-06-15 19:52:10Z

3

function adeneos_object() {
    obj[ keyx ] = $.map($( selector ),function(el){return el.value;});
}

answered Jun 15, 2013 at 19:52

adeneo

319k29 gold badges410 silver badges392 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

slebetman Over a year ago

This is how you use the map method.

oleq · Accepted Answer · 2013-06-15 20:01:47Z

1

jsPerf comes with help.

Apparently, accessing object's property each time (global_object) is slower that data acquisition and further assignment (local_variable).

However, as you see, it depends on the optimization strategy used by the particular browser (Firefox, almost equal).

answered Jun 15, 2013 at 20:01

oleq

15.9k1 gold badge40 silver badges69 bronze badges

Collectives™ on Stack Overflow

Performance of modifying an array in an object: to use a variable, or not?

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related