Introduction to objects in JavaScript_javascript skills

In JavaScript, except number, string, boolean, null and undefined, all other values ​​are objects. Objects can be declared directly through literals or created through the new operator. Unlike the Java language, properties in JavaScript objects can be dynamically added or deleted; at the same time, properties in objects can also be empty strings:

Copy code The code is as follows:

//properties in object can be added/deleted dynamically
var o = {x:1, y:2};
console.log(o);//Object {x=1, y=2}
delete o.y;
o.z = 3;
console.log(o);//Object {x=1, z=3}

//empty string is allowed as object property
var o2 = {"":88, "p":99};
console.log(o2);//Object { =88, p=99}

//for constructor function, "new" operation returns an object.
function Computer(x, y) {
this.x = x;
this.y = y;
}
var c = new Computer(126, 163);
console.log(c);//Computer {x=126, y=163}
var c2 = new Computer(126);//missing parameter value will be "undefined"
console.log(c2);//Computer {x=126, y=undefined}
c.z = 66;
console.log(c);//Computer {x=126, y=163, z=66}
delete c.y;
console.log(c);//Computer {x=126, z=66}

If the function used when using the new operator to create a new object is not a class constructor, but just an ordinary function, then JavaScript will return an empty object after executing the function:

Copy code The code is as follows:

//for pure function, "new" operation returns an empty object.
function compute(x){
console.log("execute function compute");
Return x*2;
}
var a = new compute();
console.log(a);//compute {}

Object property

Object in JavaScript has the following 3 properties:

1.prototype. Reference, pointing to the prototype object of Object. Properties in prototype objects can be inherited by Object.
2.class. A string representing the class name of Object.
3.extensible. A boolean value indicating whether dynamic addition of properties is allowed in the Object. This property is only valid in ECMAScript 5.

Property attribute

Property in Object also has 3 attributes:

1.writable. Whether the property is writable.
2.enumerable. Whether the property will be enumerated when using the for/in statement.
3. configurable. Whether the properties of this property can be modified and whether the property can be deleted.