Is there any way to map keys and values ​​in an array using Javascript? In my opinion, it is something similar to jQuery .map(), but instead of mapping only the value, also "maps" the keys.

Suppose I have the following array:

var names = [ 1, 2, 3, 4, 5 ];

And I like to use a function called numberToName() that I created and generate another array from this, and the result should be something like this:

var names = { "one": 1, "two": 2, "three": 3, "four": 4, "five": 5 };

Currently I use the following method:

var names = [ 1, 2, 3, 4, 5 ],
    names_tmp = {},
    names_i = 0,
    names_len = names.length;

for(; names_i < names_len; names_i++) {
    names_tmp[numberToName(names[names_i])] = names[names_i];
}

The question is: is there any way (preferably native) to improve this method? I could even use jQuery without problems. Perhaps a function similar to this:

var names = jQuery.mapKeys([ 1, 2, 3, 4, 5], function(k, v) {
    return { key: numberToName(v), value: v };
});

Is there any way to map keys and values ​​in an array using Javascript? In my opinion, it is something similar to jQuery .map(), but instead of mapping only the value, also "maps" the keys.

Suppose I have the following array:

var names = [ 1, 2, 3, 4, 5 ];

And I like to use a function called numberToName() that I created and generate another array from this, and the result should be something like this:

var names = { "one": 1, "two": 2, "three": 3, "four": 4, "five": 5 };

Currently I use the following method:

var names = [ 1, 2, 3, 4, 5 ],
    names_tmp = {},
    names_i = 0,
    names_len = names.length;

for(; names_i < names_len; names_i++) {
    names_tmp[numberToName(names[names_i])] = names[names_i];
}

The question is: is there any way (preferably native) to improve this method? I could even use jQuery without problems. Perhaps a function similar to this:

var names = jQuery.mapKeys([ 1, 2, 3, 4, 5], function(k, v) {
    return { key: numberToName(v), value: v };
});

• javascript
• jquery
• arrays
• dictionary

2 Answers 2

You're looking for reduce:

var names = [1, 2, 3, 4, 5].reduce(function(obj, k) {
     return obj[numberToName(k)] = k, obj;
}, {});

return obj[numberToName(k)] = k, obj is a shorthand (and admittedly less readable) way to write assignment + return:

     obj[numberToName(k)] = k;
     return obj;

A simple forEach will do the job too:

names = {};
[1, 2, 3, 4, 5].forEach(function(k) {
   names[numberToName(k)] = k
})

You can also use jquery's $.each in the same way if you want.

sure is, (as of IE9):

var nums={};
[ 1, 2, 3, 4, 5].forEach(function(v, i) {
    this[numberToName(v)]=v; 
}, nums);

nums;

EDIT: added an index to make it easier to tell what's going on.

EDIT: made it perfect by using forEach, which even though it's not as close to $'s .map(), does run about 3% faster than [].map. (thanks to thg435 for the tip!)