JavaScript associative array by variable

Question

I'd like to pass a variable into the key of my monthHash variable here:

 var monthHash = new Array();
  monthHash["JAN"] = "Jan";
  monthHash["FEB"] = "Feb";
  ...
  monthHash["NOV"] = "Nov";
  monthHash["DEV"] = "Dec";

Such that I can do this:

alert(monthHash[the_variable]);

Instead of using a switch case to go through this.

When I try, however, I get an error. Is there a way I can have a variable indicate a string identifier for the key in JavaScript?

Daniel Vassallo · Accepted Answer · 2010-06-22 21:21:03Z

6

The only case that I can see where your code can generate an error is when the_variable is undefined (where you would receive a ReferenceError).

However, Array is not meant to be used for key/value pairs. You should use an object instead:

var monthHash = {};
monthHash['JAN'] = 'Jan';
monthHash['FEB'] = 'Feb';
monthHash['NOV'] = 'Nov';
monthHash['DEC'] = 'Dec';

var the_variable = 'NOV';

alert(monthHash[the_variable]);  // alerts 'Nov'

answered Jun 22, 2010 at 21:21

Daniel Vassallo

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Comments

Nightfirecat · Accepted Answer · 2013-11-22 23:59:01Z

2

Declare it to be an object:

var monthHash = {};
monthHash["JAN"] = ..;

or

var monthHash = {jan: "...", ...}

var x = "jan";
alert(monthHash[x]);

edited Nov 22, 2013 at 23:59

Nightfirecat

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answered Jun 22, 2010 at 21:05

jvliwanag

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1 Comment

dkretz Over a year ago

Right - see a lot of literature (quirksmode.org/js/associative.html) on why js arrays are not associative arrays, but use an Object instead. (But I'd use "var monthHash = new Object();)

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