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Map Object (JavaScript)

A collection of key/value pairs.

mapObj = new Map()

The keys and values in the collection may be of any type. If you add a value to the collection using an existing key, the new value will replace the old value.

The following table lists the properties of the Map object.

Property

Description

constructor

Specifies the function that creates a map.

prototype

Returns a reference to the prototype for a map.

size

Returns the number of elements in a map.

The following table lists the methods of the Map object.

Method

Description

clear

Removes all elements from a map.

delete

Removes a specified element from a map.

forEach

Performs the specified action for each element in a map.

get

Returns a specified element from a map.

has

Returns true if the map contains a specified element.

set

Adds a new element to a map.

toString

Returns a string representation of a map.

valueOf

Returns the primitive value of the specified object.

The following example shows how to add members to a Map and then retrieve them.

var m = new Map();
m.set(1, "black");
m.set(2, "red");
m.set("colors", 2);
m.set({x:1}, 3);

m.forEach(function (item, key, mapObj) {
    document.write(item.toString() + "<br />");
});

document.write("<br />");
document.write(m.get(2));

// Output:
// black
// red
// 2
// 3
//
// red

Supported in the Internet Explorer 11 standards document mode. Also supported in Store apps (Windows 8.1 and Windows Phone 8.1). See Version Information. Not supported in the following document modes: Quirks, Internet Explorer 6 standards, Internet Explorer 7 standards, Internet Explorer 8 standards, Internet Explorer 9 standards, Internet Explorer 10 standards. Not supported in Windows 8.

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