JavaScript ES5-objektmetoder

Indholdsfortegnelse

ECMAScript 5 (2009) tilføjede en masse nye objektmetoder til JavaScript.

Håndtering af objekter

// Create object with an existing object as prototype
Object.create()

// Adding or changing an object property
Object.defineProperty(object, property, descriptor)

// Adding or changing object properties
Object.defineProperties(object, descriptors)

// Accessing Properties
Object.getOwnPropertyDescriptor(object, property)

// Returns all properties as an array
Object.getOwnPropertyNames(object)

// Accessing the prototype
Object.getPrototypeOf(object)

// Returns enumerable properties as an array
Object.keys(object)

Beskyttelse af genstande

// Prevents adding properties to an object
Object.preventExtensions(object)

// Returns true if properties can be added to an object
Object.isExtensible(object)

// Prevents changes of object properties (not values)
Object.seal(object)

// Returns true if object is sealed
Object.isSealed(object)

// Prevents any changes to an object
Object.freeze(object)

// Returns true if object is frozen
Object.isFrozen(object)

Ændring af en ejendomsværdi

Syntaks

Object.defineProperty(object, property, {value : value})

Dette eksempel ændrer en egenskabsværdi:

Eksempel

const person = {
  firstName: "John",
  
  lastName : "Doe",
  language : "EN" 
};
// Change a property
Object.defineProperty(person, "language", 
  {value : "NO"});

Prøv det selv →

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript Object.defineProperty()</h2>

<p>This example changes a property value.</p>

<p id="demo"></p>

<script>
// Create an object:
const person = {
  firstName: "John",
  lastName: "Doe",
  language: "EN" 
};

// Change a property
Object.defineProperty(person, "language", {value:"NO"})
document.getElementById("demo").innerHTML = person.language;
</script>

</body>
</html>

Ændring af metadata

ES5 tillader, at følgende egenskabsmetadata ændres:

writable : true      // Property value can be changed
enumerable : true    // Property can be enumerated
configurable : true  // Property can be reconfigured

writable : false     // Property value can not be changed
enumerable : false   // Property can be not enumerated
configurable : false // Property can be not reconfigured

ES5 gør det muligt at ændre gettere og sættere:

// Defining a getter
get: function() { return language }
// Defining a setter
set: function(value) { language = value }

Dette eksempel gør sproget skrivebeskyttet:

Object.defineProperty(person, "language", {writable:false});

Dette eksempel gør, at sproget ikke kan tælles:

Object.defineProperty(person, "language", {enumerable:false});

Liste over alle ejendomme

Dette eksempel viser alle egenskaber for et objekt:

Eksempel

const person = {
  firstName: "John",
  
  lastName : "Doe",
  language : "EN" 
};

  Object.defineProperty(person, "language", {enumerable:false});
Object.getOwnPropertyNames(person);  // Returns an array of 
  properties

Prøv det selv →

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript Object.getOwnPropertyNames()</h2>

<p>This example list the properties of an object.</p>

<p id="demo"></p>

<script>
// Create an object:
const person = {
  firstName: "John",
  lastName: "Doe",
  language: "EN"
}

// Change Property
Object.defineProperty(person, "language", {enumerable:false});

// Display Properties
document.getElementById("demo").innerHTML = Object.getOwnPropertyNames(person);
</script>

</body>
</html>

Fortegnelse over talrige egenskaber

Dette eksempel viser kun de talrige egenskaber for et objekt:

Eksempel

const person = {
  firstName: "John",
  
  lastName : "Doe",
  language : "EN" 
};

  Object.defineProperty(person, "language", {enumerable:false});
Object.keys(person);  // Returns an array 
  of enumerable  
  properties

Prøv det selv →

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript Object.keys()</h2>

<p>This example list the enumerable properties of an object.</p>

<p id="demo"></p>

<script>
// Create an object:
const person = {
  firstName: "John",
  lastName: "Doe",
  language: "EN"
}

// Change Property
Object.defineProperty(person, "language", {enumerable:false});

// Display Properties
document.getElementById("demo").innerHTML = Object.keys(person);
</script>

</body>
</html>

Tilføjelse af en ejendom

Dette eksempel tilføjer en ny egenskab til et objekt:

Eksempel

 // Create an object:
const person = {
  firstName: "John",
  lastName : 
  "Doe",
  language : "EN"
};
// Add a property
Object.defineProperty(person, "year", 
  {value:"2008"});

Prøv det selv →

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript Object.defineProperty()</h2>

<p>This example adds a new property to an object.</p>

<p id="demo"></p>

<script>
// Create an object:
const person = {
  firstName: "John",
  lastName: "Doe",
  language: "EN"
};

// Add a property
Object.defineProperty(person, "year", {value:"2008"})
document.getElementById("demo").innerHTML = person.year;
</script>

</body>
</html>

Tilføjelse af gettere og settere

Metoden Object.defineProperty() kan også bruges til at tilføje Getters og Settere:

Eksempel

//Create an object
const person = {firstName:"John", lastName:"Doe"};

// Define a getter
Object.defineProperty(person, "fullName", {
  get: 
function () {return this.firstName + " " + this.lastName;}
});

Prøv det selv →

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript Object.defineProperty()</h2>

<p>This example uses the defineProperty() method to add a getter and a setter.</p>

<p id="demo"></p>

<script>
// Create an object:
const person = {firstName:"John", lastName:"Doe"};

// Define a getter
Object.defineProperty(person, "fullName", {
  get: function () {return this.firstName + " " + this.lastName;}
});

// Display full name
document.getElementById("demo").innerHTML = person.fullName;
</script>

</body>
</html>

Et modeksempel

Eksempel

// Define object
const obj = {counter:0};

// Define setters
Object.defineProperty(obj, "reset", {
  get : function () {this.counter = 0;}
});
Object.defineProperty(obj, "increment", {
  get : function () {this.counter++;}
});
Object.defineProperty(obj, "decrement", {
  get : function () {this.counter--;}
});
Object.defineProperty(obj, "add", {
  set : function (value) {this.counter += value;}
});
Object.defineProperty(obj, "subtract", {
  set : function (i) {this.counter -= i;}
});

// Play with the counter:
obj.reset;
obj.add = 5;
obj.subtract = 1;
obj.increment;
obj.decrement;

Prøv det selv →

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript Getters and Setters</h2>

<p>Perfect for creating counters:</p>

<p id="demo"></p>

<script>
// Define an object
const obj = {counter:0};

// Define Setters and Getters
Object.defineProperty(obj, "reset", {
  get : function () {this.counter = 0;}
});
Object.defineProperty(obj, "increment", {
  get : function () {this.counter++;}
});
Object.defineProperty(obj, "decrement", {
  get : function () {this.counter--;}
});
Object.defineProperty(obj, "add", {
  set : function (value) {this.counter += value;}
});
Object.defineProperty(obj, "subtract", {
  set : function (value) {this.counter -= value;}
});

// Play with counter:
obj.reset;
obj.add = 5;
obj.subtract = 1;
obj.increment;
obj.decrement;
document.getElementById("demo").innerHTML = obj.counter;
</script>

</body>
</html>