Delete entries from an associative array (JavaScript)

Question

I currently have a problem in deleting entries from an associative array in JS.

I tried this:

  myArray['key'] = value;
  myArray['key1'] = value1;

  ...

  delete myArray['key'];

But I get following results in my application:

  [ undefined, { key1: 'value1', key2: 'value2' }, undefined,
    { key1: 'value1', key2: 'value2' }, undefined, undefined ]

How can I delete the whole entry, key and value? I found the method splice() but I think it uses a different index. I wasn't able to delete the entries I want by passing the key to splice().

Javascript doesn't have associative arrays. It has objects, which are collections of names and values, and arrays, which are objects with a special length property and some handy methods. — RobG
– RobG, Commented May 23, 2011 at 20:56

Felix Kling · Accepted Answer · 2011-05-23 19:50:54Z

9

It seems you are mixing arrays and objects. Associative arrays should be realized with objects:

myArray = {};
myArray['key'] = value;
myArray['key1'] = value1;

It is a bit confusing though because in your output, the objects don't have key anymore (so it worked), but the array containing those objects as undefined values. I cannot see how delete myArray['key']; is related to your output and which variable now contains which value (please clarify).

But it looks like you did something like:

var container = new Array(6);
container[1] = myArray;
container[3] = myArray;

This will initialize the array with 6 undefined values (sort of) and then set the second and forth value to something else.

If you want to use that "array" as associative array, you should declare it as object too:

var container = {};

Please post more code if you need a better answer.

Update: Yes, you should declare displayedWidgets as object:

var widgets = {
    displayedWidgets: {},

    clear: function() {
        this.displayedWidgets = {};
    },

    add: function(widget) {  
        this.displayedWidgets[widget.id] = widget;
    },

    addArray: function(newWidgets) {
        // note that `each` is only available in newer browsers,
        // just loop over the array
        for(var i = newWidgets.length; i--; ) {
            this.add(newWidgets[i]);
        }
    },

    remove: function(widgetId) {
        if (widgetId in this.displayedWidgets) {
            delete this.displayedWidgets[widgetId];
        }
    }
};

edited May 23, 2011 at 19:50

answered May 23, 2011 at 19:20

Felix Kling

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4 Comments

ffraenz Over a year ago

The 'loop over the array' makes problems... How to get an entry of displayedWidgets by index, not by key? The key is the id of the widget what comes from the database.. so key != index.

Ruan Mendes Over a year ago

+1: In JS, unlike PHP, arrays are not to be used as a hash map. The solution suggested is the best thing to do, displayedWidgets should be an object (which is a hash map), not an array which is to be used only when you need to index items by an interger, not a string.

Felix Kling Over a year ago

@FFraenz: You cannot have both (with one data structure). If you also need some kind of order of the widgets, then you need another array, where you e.g. add the key. Or you base everything on indices only. Or I don't understand the problem... what do you need the index for?

ffraenz Over a year ago

I think I have to study a bit these things. Thank you for your fast help!

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