Native js constructor

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javascript is an object-based language, which contains 5 Native data type:

• number (numeric type)

• boolean (Boolean type)

• string(string type)

• null(empty)

• undefined(undefined)

  other than , everything else is an object, and a function is also an object;

function fn(){
  //这是一个函数声明，函数是一个特殊的对象}

Constructor function definition
The constructor is an ordinary function , there is no difference from other functions, it can be understood as function == constructor, it is just a conceptual definition, use it to instantiate objects.

For JavaScript’s built-in objects, Object, Array, Date, etc. are all constructors.

function Fn(){}var f = new Fn() //实例化对象

The object returned by using the new operator is not necessarily the instance itself. You can also use return to change the return value in the constructor:

function Obj() {
  this.a = 1;  return { a: 2 };
}var o = new Obj(); // o并不是Obj的实例console.log(o.a); // 输出2

As mentioned earlier, the function is also an object. In JavaScript Among the built-in objects, all function objects are instances of the Function constructor, such as: Object, Array, etc.

You can use the instanceof operator to verify

• #The instanceof operator returns whether a specified object is an instance of a class, in the format: A instanceof B. Among them, the left operand must be an object, and the right operand must be a class (constructor);

• Judgment process: If function B is found in the prototype chain of object A, Then the instanceof operator will return true, otherwise it will return false.

alert(Function instanceof Function); // Function函数对象 本身就是自己的一个实例alert(Object instanceof Function); // Object函数对象 是 Function构造函数的一个实例alert(arr instanceof Array);

             

javascript is an object-based language, which contains 5 native data types:

• number( Numeric type)

• boolean(Boolean type)

• string(String type)

• null (empty)

• undefined (undefined)

  In addition, everything else is an object, and the function is also an object;

function fn(){
  //这是一个函数声明，函数是一个特殊的对象}

Constructor function definition
The constructor is an ordinary function, no different from other functions, it can be understood as function == constructor, it It's just a conceptual definition, used to instantiate objects.

For JavaScript’s built-in objects, Object, Array, Date, etc. are all constructors.

function Fn(){}var f = new Fn() //实例化对象

The object returned by using the new operator is not necessarily the instance itself. You can also use return to change the return value in the constructor:

function Obj() {
  this.a = 1;  return { a: 2 };
}var o = new Obj(); // o并不是Obj的实例console.log(o.a); // 输出2

As mentioned earlier, the function is also an object. In JavaScript Among the built-in objects, all function objects are instances of the Function constructor, such as: Object, Array, etc.

You can use the instanceof operator to verify

• #The instanceof operator returns whether a specified object is an instance of a class, in the format: A instanceof B. Among them, the left operand must be an object, and the right operand must be a class (constructor);

• Judgment process: If function B is found in the prototype chain of object A, Then the instanceof operator will return true, otherwise it will return false.

alert(Function instanceof Function); // Function函数对象 本身就是自己的一个实例alert(Object instanceof Function); // Object函数对象 是 Function构造函数的一个实例alert(arr instanceof Array);

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