Function function

Function

Every JavaScript Functions are actually one Function object . function (function(){}).constructor === Function // true We can get this conclusion .

Instance attributes

arguments

Is an array of class objects corresponding to the parameters passed to the function .

function func1(a, b, c) {
    
  console.log(arguments[0]);
  // expected output: 1

  console.log(arguments[1]);
  // expected output: 2

  console.log(arguments[2]);
  // expected output: 3
}

func1(1, 2, 3);

Function.length

length Property indicates the number of formal parameters of the function .

function func1() {
    }

function func2(a, b) {
    }

console.log(func1.length);
// expected output: 0

console.log(func2.length);
// expected output: 2

Example method

Function.length

length Property indicates the number of formal parameters of the function .

function func1() {
    }

function func2(a, b) {
    }

console.log(func1.length);
// expected output: 0

console.log(func2.length);
// expected output: 2

apply() The grammar of

call And apply The context of the setting function used for display , Both methods work the same way by binding objects to this, It's just different in passing parameters .

call and apply It's all about change this The direction of . The effect is the same , It's just that the way to pass the parameters is different .

call You can receive a list of parameters

apply Accept only one parameter array .

And bind Different call/apply The function will be executed immediately

function show(title) {
    
  console.log(`${
      title + this.name}`);
}
let lisi = {
    
  name: " Li Si ",
};
let wangwu = {
    
  name: " Wang Wu ",
};
show.call(lisi, " user 1：");
show.apply(wangwu, [" user 2："]);

//  user 1： Li Si 
//  user 2： Wang Wu 

Function.prototype.bind()

bind() Method creates a new function , stay bind() When called , Of this new function this Is specified as bind() The first parameter of , The rest of the parameters will be the parameters of the new function , For calling .

const module = {
    
  x: 42,
  getX: function () {
    
    return this.x;
  },
};

const unboundGetX = module.getX;
console.log(unboundGetX()); // The function gets invoked at the global scope
// expected output: undefined

const boundGetX = unboundGetX.bind(module);
console.log(boundGetX());
// expected output: 42

Function.prototype.call()

call() Method uses a specified this Value and one or more parameters given separately to call a function .

function Product(name, price) {
    
  this.name = name;
  this.price = price;
}

function Food(name, price) {
    
  Product.call(this, name, price);
  this.category = "food";
}

console.log(new Food("cheese", 5).name);
// expected output: "cheese"

Function.prototype.toString()

toString() Method returns a string representing the source code of the current function .

function sum(a, b) {
    
  return a + b;
}

console.log(sum.toString());
// expected output: "function sum(a, b) {
    
// return a + b;
// }"

console.log(Math.abs.toString());
// expected output: "function abs() { [native code] }"

Function.prototype.bind()

Function.prototype.bind()