JavaScript Object API
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The document explains methods for creating and manipulating JavaScript objects, including Object.create(), Object.defineProperties(), and Object.defineProperty(). It details how to define and modify object properties, retrieve properties, and copy properties from one object to another using Object.assign(). Additionally, it discusses how to check if an object is sealed with Object.isSealed().
![JavaScript OBJECT
Object.create() method creates a new object with the specified prototype
object and properties.
Syntax
Object.create(proto[, propertiesObject])
function Car (desc) {
this.desc = desc;
this.color = "red";
}
Car.prototype = {
getInfo: function() {
return 'A ' + this.color + ' ' + this.desc + '.';
}
};
//instantiate object using the constructor function
var car = Object.create(Car.prototype);
car.color = "blue";
alert(car.getInfo());
Object.defineProperties() method defines new or modifies existing
properties directly on an object, returning the object.
Syntax
Object.defineProperties(obj, props)
var obj = {};
Object.defineProperties(obj, {
'property1': {
value: true,](https://image.slidesharecdn.com/jsobject-220601064700-ac92cba4/95/JavaScript-Object-API-1-638.jpg)
![configurable: true
});
Object.entries() method returns an array of a given object's own enumerable
property [key, value] pairs, in the same order as that provided by a for...in loop
(the difference being that a for-in loop enumerates properties in the prototype
chain as well).
Syntax
Object.entries(obj)
var obj = { soap: 'bar', baz: 42 };
console.log(Object.entries(obj)); // [ [soap, 'bar'], ['baz', 42] ]
Object.keys() method returns an array of a given object's own enumerable
properties, in the same order as that provided by a for...in loop (the difference
being that a for-in loop enumerates properties in the prototype chain as well).
Syntax
Object.keys(obj)
Parameters
obj
The object of which the enumerable own properties are to be returned.
var arr = ['a', 'b', 'c'];
console.log(Object.keys(arr)); // console: ['0', '1', '2']
Object.assign() method is used to copy the values of all enumerable own
properties from one or more source objects to a target object. It will return the
target object.](https://image.slidesharecdn.com/jsobject-220601064700-ac92cba4/95/JavaScript-Object-API-3-638.jpg)
JavaScript Object API
- 1. JavaScript OBJECT Object.create() method creates a new object with the specified prototype object and properties. Syntax Object.create(proto[, propertiesObject]) function Car (desc) { this.desc = desc; this.color = "red"; } Car.prototype = { getInfo: function() { return 'A ' + this.color + ' ' + this.desc + '.'; } }; //instantiate object using the constructor function var car = Object.create(Car.prototype); car.color = "blue"; alert(car.getInfo()); Object.defineProperties() method defines new or modifies existing properties directly on an object, returning the object. Syntax Object.defineProperties(obj, props) var obj = {}; Object.defineProperties(obj, { 'property1': { value: true,
- 2. writable: true }, 'property2': { value: 'Hello', writable: false } // etc. etc. }); Object.defineProperty() method defines a new property directly on an object, or modifies an existing property on an object, and returns the object. Syntax Object.defineProperty(obj, prop, descriptor) Parameters obj The object on which to define the property. prop The name of the property to be defined or modified. descriptor The descriptor for the property being defined or modified. var o = {}; // Creates a new object // Example of an object property added // with defineProperty with a data property descriptor Object.defineProperty(o, 'a', { value: 37, writable: true, enumerable: true,
- 3. configurable: true }); Object.entries() method returns an array of a given object's own enumerable property [key, value] pairs, in the same order as that provided by a for...in loop (the difference being that a for-in loop enumerates properties in the prototype chain as well). Syntax Object.entries(obj) var obj = { soap: 'bar', baz: 42 }; console.log(Object.entries(obj)); // [ [soap, 'bar'], ['baz', 42] ] Object.keys() method returns an array of a given object's own enumerable properties, in the same order as that provided by a for...in loop (the difference being that a for-in loop enumerates properties in the prototype chain as well). Syntax Object.keys(obj) Parameters obj The object of which the enumerable own properties are to be returned. var arr = ['a', 'b', 'c']; console.log(Object.keys(arr)); // console: ['0', '1', '2'] Object.assign() method is used to copy the values of all enumerable own properties from one or more source objects to a target object. It will return the target object.
- 4. Syntax Object.assign(target, ...sources) Parameters target The target object. sources The source object(s). var obj = { a: 1 }; var copy = Object.assign({}, obj); console.log(copy); // { a: 1 } Object.isSealed() method determines if an object is sealed. Syntax Object.isSealed(obj) Parameters obj The object which should be checked. var empty = {}; Object.isSealed(empty); // === false // If you make an empty object non-extensible, // it is vacuously sealed. Object.preventExtensions(empty); Object.isSealed(empty); // === true