JS Basic Knowledge Point Collection

JS Basic knowledge Point Collection JS common base types

 function show(x) {Console. log (typeof(x));//undefined        Console. log (typeof(Ten));// number        Console. log (typeof(' abc '));//String        Console. log (typeof(true));//Boolean        Console. log (typeof([]));//Object        Console. log (typeof( function () {        }));//function        Console. log (typeof([1,' A ',true]));//object        Console. log (typeof({a:TenB: -}));//object        Console. log (typeof(NULL));//object        Console. log (typeof(New  Number(Ten)));//object} show ();

Value type: Undefined, number, String, Boolean
Reference types: Functions, arrays, objects, null (all reference types are objects, objects are collections of properties)

JS Prototype and prototype chain

 function Fn() {} Fn.prototype.name =' Wang Fu '; Fn.prototype.getYear = function () {return 1988; };varfn =NewFn ();Console. log (Fn.name);Console. log (Fn.getyear ());

FN is fnnew out of the object, FN.Proto = = = Fn.prototype

JS prototype chain

 function  foo   ()   {} var  f1 = new  Foo (); //f1.a = ten;  Foo.prototype.a = 100 ; foo.prototype.b = 200 ; console . log (f1.a); //100  console . log (f1.b); //200  

When the F1 is assigned a value

    console.log(f1.a);//10    console.log(f1.b);//200

Prototype chain:访问一个对象的属性时，先在基本属性中查找，如果没有，再沿着__proto__这条链向上找，这就是原型链

JS prototype chain inheritance

A = {a: function () {Console. log (' A '); }} b= {B: function () {Console. log (' B '); }} a.a ();//aB.B ();//b    Object. setprototypeof (A, b);//Give the prototype of B to aA.B ();//b

JS context

提到js的上下文先说下this关键字
The value of this in the function is determined when the function is actually called and the function definition cannot be determined.

Scenario 1: Constructors

    function A() { This. A =' A '; This. Hello = function () {Console. log ( This. a);//a}Console. log ( This);//{a: "A"}}varA =NewA (); A.hello ();

If the function is used as a constructor, then this represents the object it is about to be new.

Scenario 2: Function as a property of an object
Console.log (THIS.A);//a

Scenario 3: Function calls

with call or apply

  var B = {        ‘b‘    }    varfunction () {        console.log(this.b);    }    A.call(B);//b

When a function is called by call and apply, the value of this takes the value of the passed-in object.

Scenario 4: Function global & Call common functions
In the global environment and normal function calls, it is the window

JS Basic Knowledge Point Collection