How to create a simple map using JavaScript/JQuery [duplicate]

Edit: Out of date answer, ECMAScript 2015 (ES6) standard javascript has a Map implementation, read here for more info: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map

var map = new Object(); // or var map = {};
map[myKey1] = myObj1;
map[myKey2] = myObj2;

function get(k) {
    return map[k];
}

//map[myKey1] == get(myKey1);

Just use plain objects:

var map = { key1: "value1", key2: "value2" }
function get(k){
  return map[k];
}

function Map() {
    this.keys = new Array();
    this.data = new Object();

    this.put = function (key, value) {
        if (this.data[key] == null) {
            this.keys.push(key);
        }
        this.data[key] = value;
    };

    this.get = function (key) {
        return this.data[key];
    };

    this.remove = function (key) {
        this.keys.remove(key);
        this.data[key] = null;
    };

    this.each = function (fn) {
        if (typeof fn != 'function') {
            return;
        }
        var len = this.keys.length;
        for (var i = 0; i < len; i++) {
            var k = this.keys[i];
            fn(k, this.data[k], i);
        }
    };

    this.entrys = function () {
        var len = this.keys.length;
        var entrys = new Array(len);
        for (var i = 0; i < len; i++) {
            entrys[i] = {
                key: this.keys[i],
                value: this.data[i]
            };
        }
        return entrys;
    };

    this.isEmpty = function () {
        return this.keys.length == 0;
    };

    this.size = function () {
        return this.keys.length;
    };
}

This is an old question, but because the existing answers could be very dangerous, I wanted to leave this answer for future folks who might stumble in here...

The answers based on using an Object as a HashMap are broken and can cause extremely nasty consequences if you use anything other than a String as the key. The problem is that Object properties are coerced to Strings using the .toString method. This can lead to the following nastiness:

function MyObject(name) {
  this.name = name;
};
var key1 = new MyObject("one");
var key2 = new MyObject("two");

var map = {};
map[key1] = 1;
map[key2] = 2;

If you were expecting that Object would behave in the same way as a Java Map here, you would be rather miffed to discover that map only contains one entry with the String key [object Object]:

> JSON.stringify(map);
{"[object Object]": 2}

This is clearly not a replacement for Java's HashMap. Bizarrely, given it's age, Javascript does not currently have a general purpose map object. There is hope on the horizon, though: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map although a glance at the Browser Compatability table there will show that this isn't ready to used in general purpose web apps yet.

In the meantime, the best you can do is:

Deliberately use Strings as keys. I.e. use explicit strings as keys rather than relying on the implicit .toString-ing of the keys you use.
Ensure that the objects you are using as keys have a well-defined .toString() method that suits your understanding of uniqueness for these objects.
If you cannot/don't want to change the .toString of the key Objects, when storing and retrieving the entries, convert the objects to a string which represents your understanding of uniqueness. E.g. map[toUniqueString(key1)] = 1

Sometimes, though, that is not possible. If you want to map data based on, for example File objects, there is no reliable way to do this because the attributes that the File object exposes are not enough to ensure its uniqueness. (You may have two File objects that represent different files on disk, but there is no way to distinguish between them in JS in the browser). In these cases, unfortunately, all that you can do is refactor your code to eliminate the need for storing these in a may; perhaps, by using an array instead and referencing them exclusively by index.

var map = {'myKey1':myObj1, 'mykey2':myObj2};
// You don't need any get function, just use
map['mykey1']

How to create a simple map using JavaScript/JQuery [duplicate]

Related

Recent Posts