Populate a javascript array shorthand for keys like php

Question

In Javascript, know I can set an array so that the key is a autonumbered (starting at 0) assigned array:

var d_names = new Array("Sunday", "Monday", "Tuesday", 
              "Wednesday", "Thursday", "Friday", "Saturday");

// Key for Sunday is '0'

and if I want to assign keys, I could do:

    var d_names={};
    d_names[5]="Sunday";
    d_names[6]="Monday";
    d_names[7]="Tuesday";
    d_names[8]="Wednesday";
    d_names[9]="Thursday";
    d_names[10]="Friday";
    d_names[11]="Saturday";

    // Key for Sunday is '5'

But is there a shorthand way to assign the keys like in PHP?

var d_names = new Array(5=>"Sunday", 6=>"Monday", 7=>"Tuesday", 8=>"Wednesday", 
            9=>"Thursday", 10=>"Friday", 11=>"Saturday"); 

// Doesn't work

Javascript does not support associative arrays. You can use, however, an object. Albeit the syntax is different. — Tivie, Nov 04 '12 at 14:01
To whoever had reviewed the suggested edit: please don't approve it as is, if it overwrites changes from a later edit. — , Nov 04 '12 at 14:05

David Pärsson · Accepted Answer · 2012-11-04T14:11:42.743

11

What you want is an object:

var d_names = {
    5: "Sunday",
    6: "Monday"
    //...
};

You can then get "Sunday" like this:

var sunday = d_names[5];

edited Nov 04 '12 at 14:11

answered Nov 04 '12 at 14:00

David Pärsson

6,038
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11

Javascript does not support Associative Arrays... that's an object! – Tivie Nov 04 '12 at 14:00
True, I'm updating my answer. Since JavaScript objects can be _used_ as associative arrays, it's an easy mistake to make. – David Pärsson Nov 04 '12 at 14:06
Okay, I understand! Then, `answer=d_names[5]` (if it were an associative array), what would be the javascript equivalent syntax to get `answer` on key 5? – Sablefoste Nov 04 '12 at 14:09
The same syntax. I'm updating my answer. – David Pärsson Nov 04 '12 at 14:13
3

There is one small issue with this - it's not exactly the same thing as an Array. For example, it has no length property, and you can't push() new values onto the end. If you don't need these (or other) Array-specific features, then this is fine. – CupawnTae Nov 04 '12 at 14:16

lucideer · Answer 2 · 2012-11-04T14:13:09.080

In PHP, an array with manually defined keys (as opposed to consecutive integers beginning with 0) is called an "associative array" - this is what you have in your example above with '=>' delimiting keys and values.

In Javascript, an "associative array" is technically an "object" (though everything in JS is an object - that's a more detailed topic though).

Shorthand for an "indexed array" (consecutive integer keys) in JS is:

var d_names = [
  'Sunday',
  'Monday',
  // etc.
];

whereas shorthand for an object (like an associative array) in JS is:

var d_names = {
  5: 'Sunday',
  6: 'Monday',
  // etc.
};

You should however be careful when using indexed arrays -vs- objects/associative in Javascript. Javascript is not PHP, and the fact that "everything is an object" has repercussions when looping. A notable difference is that for(var i=0; i<arr.length; ++i){} iterates over an arrays keys but for(var x in obj) {} iterates over an objects "members" which can differ depending on environment/browser/etc.

charlietfl · Answer 3 · 2012-11-04T14:39:51.127

1

The following in php:

echo json_encode(new Array(5=>"Sunday", 6=>"Monday", 7=>"Tuesday",...11=>"Saturday"));

Will produce JSON that looks like

   {"5":"Sunday","6":"Monday" , "7":"Tuesday"..."11":"Saturday"}

If sent via ajax and result is json parsed it will return an object:

 obj= { "5": "Sunday", "6": "Monday",....  "11": "Saturday"}

Now you can access using javascript object notation:

 alert( obj['5'] )/* SUnday*/

edited Nov 04 '12 at 14:39

answered Nov 04 '12 at 14:15

charlietfl

170,828
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Your 2nd code block doesn't look right. You've fed in an associative array with string values but it's returning an indexed array with objects (with string values). – lucideer Nov 04 '12 at 14:16
Ah, apologies. One more comment on your edit (I think you had this correct previously) - JSON is "stricter" than Javascript in that it doesn't allow integer keys - so PHP will output the keys wrapped in double-quotes. This is purely for JSON though, so somewhat irrelevant to the OP, but no harm mentioning it - it's tripped me up a lot in the past. – lucideer Nov 04 '12 at 14:33
Really? You may have thought me something new... /goes off to research. – lucideer Nov 04 '12 at 14:37
@lucideer numbers are valid however as values. I never use numeric keys – charlietfl Nov 04 '12 at 14:40

score 1 · Answer 4 · answered Nov 04 '12 at 14:24

There are no associative arrays in JavaScript. You have two choices:

A simple object, used as a (unsorted!) key-value map - easy to write as a literal, also JSON syntax:

{
    "5": "Sunday",
    "6": "Monday",
    "7": "Tuesday",
    "8": "Wednesday",
    "9": "Thursday",
    "10": "Friday",
    "11": "Saturday"    
}

Or you can use a sparse Array, i.e. with no values for the properties 0 to 4. You can easily create it via

var arr = new Array(5); // creates an empty array object with length 5
arr.push("Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday");

which is equivalent to the literal

[,,,,, "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"]

very good link on the dangers of trying to use associative arrays in Javascript. — Sablefoste, Nov 04 '12 at 14:26

score 0 · Answer 5 · answered Nov 04 '12 at 14:04

Not exactly but you can use an Object

var obj = {

5:"Sunday",
6:"Monday",
7:"Tuesday",
8:"Wednesday",
9:"Thursday",
10:"Friday",
11:"Saturday"    
}

If want to use array

var arr = [];
arr[4] = undefined;
arr.push("Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday");

score 0 · Answer 6 · answered Nov 04 '12 at 14:06

0

You can achieve that with this and some other tricks

 var d_names = [,,,,,"Sunday", "Monday", "Tuesday", 
          "Wednesday", "Thursday", "Friday", "Saturday"];

 alert(d_names[5]); //prints "Sunday"

answered Nov 04 '12 at 14:06

codingbiz

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Thank you for the response. But this was more of a 'what if'; The days could have been names of pieces of fruit or something else. I am using an index which may not be in numerical order. I have just been fuzzy on the array vs. object thing, but some of the other answers have helped too. – Sablefoste Nov 04 '12 at 14:16

Populate a javascript array shorthand for keys like php

6 Answers6