Associative arrays in Javascript?

Question

Currently, I am creating a 3d array in js using the following:

var arr = [["name1", "place1", "data1"],
          ["name2", "place2", "data2"],
          ["name3", "place3", "data3"]];

I can access each element using arr[0] or arr[1]. But is there anyways I can access them using a key like this: arr["name1"] should give me the first one. Any suggestions? I think I am looking for a Hashmap like functionality.

score 3 · Answer 1 · answered Oct 31 '16 at 18:23

The situation has changed in the six years since this question was asked.

Due to weak typing associative arrays can be faked in JavaScript:

>> var names = new Array();
undefined

>> names["first"] = "Dotan";
"Dotan"

>> names["last"] = "Cohen";
"Cohen"

>> for ( key in names ) { console.log(key+" "+names[key]) }
undefined
first Dotan
last Cohen

That is sometimes useful, and all browsers released since 2012 support it, but there are caveats! The array cannot be simply read back:

>> names
Array [  ]

More importantly, the array's length cannot be easily retrieved:

>> names.length
0

Therefore this is not an associative array in the sense that JavaScript would have supported it had it been intended, but rather a workaround that is often useful if for whatever reason a real JS object does not support what you need:

>> var names = {};
undefined

>> names.first = "Dotan";
"Dotan"

>> names.last = "Cohen";
"Cohen"

>> for ( key in names ) { console.log(key+" "+names[key]) }
undefined
first Dotan
last Cohen

>> names
Object { first: "Dotan", last: "Cohen" }

>> Object.keys(names).length
2

thanks for the update. 6 years after your 6 years after – horace Jan 01 '23 at 00:50 — horace, Jan 01 '23 at 00:50

score 2 · Accepted Answer · answered Aug 03 '10 at 18:28

2

The only way you could do that is by wrapping it in an object.

var arr = {
    name1 : ["name1", "place1", "data1"],
    name2 : ["name2", "place2", "data2"],
    name3 : ["name3", "place3", "data3"]
};

answered Aug 03 '10 at 18:28

ChaosPandion

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@Legend - Don't forget to accept an answer. It will make sure you keep getting quality answers in the future. *Plus it makes me look good. :)* – ChaosPandion Aug 03 '10 at 18:39
Of course... There's a 15 minute time limit to accept answers :) – Legend Aug 03 '10 at 18:50

score 1 · Answer 3 · edited Oct 06 '11 at 13:39

1

Javascript is a prototype based dynamic language. You can create objects and change their structure when you want.

var o = {name1: {place1: data1}, name2: {place2: data2}};

and access it with:

o.name1

The look-up implementation varies though and when you have a lot of properties that often changes this can be pretty slow (except in Chrome that uses a special scheme to access object properties i.e. embedded classes a-la-dynamic dispatch from smalltalk). Some libraries (e.g. MooTools) provide some hash map related structures,

edited Oct 06 '11 at 13:39

Matt

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answered Aug 03 '10 at 18:32

Alexandre Abreu

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So in this example, to access place1, would you reference it with `o.name1.place1`? and what would that give you? The value `place1` or the value `data1`? – Noble-Surfer Mar 13 '13 at 10:06

Associative arrays in Javascript?

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