get
===

The **`get`** syntax binds an object property to a function that will be called when that property is looked up. It can also be used in classes.

Try it
------

Syntax
------


```js
{ get prop() { /\* … \*/ } }
{ get [expression]() { /\* … \*/ } }
```


There are some additional syntax restrictions:

* A getter must have exactly zero parameters.
### Parameters

`prop`

The name of the property to bind to the given function. In the same way as other properties in object initializers, it can be a string literal, a number literal, or an identifier.

`expression`

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 to 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*.

An object property is either a data property or an accessor property, but it cannot simultaneously be both. Read `Object.defineProperty()` for more information. The getter syntax allows you to specify the getter function in an object initializer.


```js
const obj = {
  get prop() {
    // getter, the code executed when reading obj.prop
    return someValue;
  },
};
```


Properties defined using this syntax are own properties of the created object, and they are configurable and enumerable.

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`.


```js
const obj = {
  log: ["example", "test"],
  get latest() {
    if (this.log.length === 0) return undefined;
    return this.log[this.log.length - 1];
  },
};
console.log(obj.latest); // "test"
```


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

### Using getters in classes

You can use the exact same syntax to define public instance getters that are available on class instances. In classes, you don't need the comma separator between methods.


```js
class ClassWithGetSet {
  #msg = "hello world";
  get msg() {
    return this.#msg;
  }
  set msg(x) {
    this.#msg = `hello ${x}`;
  }
}

const instance = new ClassWithGetSet();
console.log(instance.msg); // "hello world"

instance.msg = "cake";
console.log(instance.msg); // "hello cake"
```


Getter properties are defined on the `prototype` property of the class and are thus shared by all instances of the class. Unlike getter properties in object literals, getter properties in classes are not enumerable.

Static getters and private getters use similar syntaxes, which are described in the `static` and private properties pages.

### Deleting a getter using the `delete` operator

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


```js
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()`.


```js
const o = { a: 0 };

Object.defineProperty(o, "b", {
  get() {
    return this.a + 1;
  },
});

console.log(o.b); // Runs the getter, which yields a + 1 (which is 1)
```

### Using a computed property name


```js
const expr = "foo";

const obj = {
  get [expr]() {
    return "bar";
  },
};

console.log(obj.foo); // "bar"
```

### Defining static getters


```js
class MyConstants {
  static get foo() {
    return "foo";
  }
}

console.log(MyConstants.foo); // 'foo'
MyConstants.foo = "bar";
console.log(MyConstants.foo); // 'foo', a static getter's value cannot be changed
```

### Smart / self-overwriting / lazy getters

 Getters give you a way to *define* a property of an object, but they do not
 *calculate* the property's value until it is accessed. A getter defers the cost
 of calculating the value until the value is needed. If it is never needed, you never pay
 the cost.

 An additional optimization technique to lazify or delay the calculation of a property
 value and cache it for later access are *smart* (or *memoized*) getters.
 The value is calculated the first time the getter is called, and is then cached so
 subsequent accesses return the cached value without recalculating it. This is useful in
 the following situations:

* If the calculation of a property value is expensive (takes much RAM or CPU time,
 spawns worker threads, retrieves remote file, etc.).
* If the value isn't needed just now. It will be used later, or in some case it's not
 used at all.
* If it's used, it will be accessed several times, and there is no need to
 re-calculate that value will never be changed or shouldn't be re-calculated.

**Note:** This means that you shouldn't write a lazy getter for a property whose value you
 expect to change, because if the getter is lazy then it will not recalculate the
 value.


 Note that getters are not "lazy" or "memoized" by nature; you must implement this
 technique if you desire this behavior.


 In the following example, the object has a getter as its own property. On getting the
 property, the property is removed from the object and re-added, but implicitly as a data
 property this time. Finally, the value gets returned.


```js
const obj = {
  get notifier() {
    delete this.notifier;
    this.notifier = document.getElementById("bookmarked-notification-anchor");
    return this.notifier;
  },
};
```

### get vs. defineProperty

 While using the `get` keyword and `Object.defineProperty()` have
 similar results, there is a subtle difference between the two when used on
 `classes`.

 When using `get` the property will be defined on the instance's prototype,
 while using `Object.defineProperty()` the property will be defined on the
 instance it is applied to.


```js
class Example {
  get hello() {
    return "world";
  }
}

const obj = new Example();
console.log(obj.hello);
// "world"

console.log(Object.getOwnPropertyDescriptor(obj, "hello"));
// undefined

console.log(
  Object.getOwnPropertyDescriptor(Object.getPrototypeOf(obj), "hello"),
);
// { configurable: true, enumerable: false, get: function get hello() { return 'world'; }, set: undefined }
```

Specifications
--------------

| Specification |
| --- |
| ECMAScript Language Specification # sec-method-definitions |

Browser compatibility
---------------------

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See also
--------

* Working with objects guide
* Functions
* `set`
* `Object.defineProperty()`
* Object initializer
* `class`
* Property accessors
* Incompatible ES5 change: literal getter and setter functions must now have exactly zero or one arguments by Jeff Walden (2010)
* More SpiderMonkey changes: ancient, esoteric, very rarely used syntax for creating getters and setters is being removed by Jeff Walden (2010)