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    getter

    The get syntax binds an object property to a function that will be called when that property is looked up.

    Syntax

    {get prop() { ... } }
    {get [expression]() { ... } }

    Parameters

    prop
    The name of the property to bind to the given function.
    expression
    Starting with ECMAScript 6, you can also use expressions for a computed property name to bind to the given function.

    Description

    Sometimes it is desirable to allow access to a property that returns a dynamically computed value, or you may want reflect the status of an internal variable without requiring the use of explicit method calls. In JavaScript, this can be accomplished with the use of a getter. It is not possible to simultaneously have a getter bound to a property and have that property actually hold a value, although it is possible to use a getter and a setter in conjunction to create a type of pseudo-property.

    Note the following when working with the get syntax:

    A getter can be removed using the delete operator.

    Examples

    Defining a getter on new objects in object initializers

    This will create a pseudo-property latest for object obj, which will return the last array item in log.

    var log = ['test'];
    var obj = {
      get latest () {
        if (log.length == 0) return undefined;
        return log[log.length - 1]
      }
    }
    console.log (obj.latest); // Will return "test".
    

    Note that attempting to assign a value to latest will not change it.

    Deleting a getter using the delete operator

    If you want to remove the getter, you can just delete it:

    delete obj.latest;
    

    Defining a getter on existing objects using defineProperty

    To append a getter to an existing object later at any time, use Object.defineProperty().

    var o = { a:0 }
    
    Object.defineProperty(o, "b", { get: function () { return this.a + 1; } });
    
    console.log(o.b) // Runs the getter, which yields a + 1 (which is 1)

    Using a computed property name

    Note: Computed properties are experimental technology, part of the ECMAScript 6 proposal, and are not widely supported by browsers yet. This will trigger a syntax error in non-supporting environments.

    var expr = "foo";
    
    var obj = {
      get [expr]() { return "bar"; }
    };
    
    console.log(obj.foo); // "bar"

    Specifications

    Specification Status Comment
    ECMAScript 5.1 (ECMA-262)
    The definition of 'Object Initializer' in that specification.
    Standard Initial definition.
    ECMAScript 2015 (6th Edition, ECMA-262)
    The definition of 'Method definitions' in that specification.
    Standard Added computed property names.

    Browser compatibility

    Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
    Basic support 1 2.0 (1.8.1) 9 9.5 3
    Computed property names Not supported 34 (34) Not supported Not supported Not supported
    Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
    Basic support (Yes) (Yes) 1.0 (1.8.1) (Yes) (Yes) (Yes)
    Computed property names Not supported Not supported 34.0 (34.0) Not supported Not supported Not supported

    See also

    Document Tags and Contributors

    Last updated by: fscholz,
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