This is the 7th day of my participation in the August Text Challenge.More challenges in August

Variable promotion [pre-parsing]

Before the current context code is executed “top-down”, the browser will declare or define all pending “var/function” keywords

  • Knowledge with VAR is declared ahead of time
  • Function is pre-declared + assigned (definition)

EC(G) variable promotion:

// var a;
// fn1=0x000; [[scope]:EC(G)]
// var fn2

console.log(a); // undefined
fn1();
var a= 10;  / / global a = 10
function fn1(){  // Skip [variable promotion truncation already created]

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// var a;
// fn1=0x000; [[scope]:EC(G)]
// var fn2
console.log(a); // undefined
fn1();
var a= 10;  / / global a = 10
function fn1(){  // Skip [variable promotion truncation already created]

` `'// Can you do this type of problem correctly? `` `js
// EC(FN1)

    
      (fn1),ec(g)>
    // Parameter assignment: --
    // Variable promotion:
    // var a;
    
    console.log('fn1') // 'fn1'
    console.log(a); // undefined
    var a = 20;   / / private a = 20
    console.log(a);  / / 20
}
fn1();
fn2();  // Uncaught TypeError: fn2 is not a function
var fn2 = function(){ // Function expression
    console.log('fn2')
}
fn2();
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In real projects, it is recommended to use function expressions to create functions. Normal functions are declared and assigned in the variable promotion phase, while function expressions are only declared
// Function expression can specify the order of function execution.

// const fn = function(){};
// fn();
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Anonymization of functions

// Namespaces for anonymous functions

var fn = function sum() {
   console.log('OK');
};
fn();
sum();
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Self-executing function

"use strict";// -> make js use strict mode
// Self-executing function

(function anonyous(x){
    if(x<0) return;
    console.log(x);
    // recursive call
    // console.log(arguments.callee); // The function itself
    Uncaught TypeError: "Use strict" is not a functio
    // arguments.callee(x-1)
    anonyous(x-1); }) (10)
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Variable lifting function

// EC(G)
// Variable promotion:
// fn=0x000 [[scope]:EC(G)]
// [in older browsers]
// sum=0x001 [[scope]:EC(G)]
// [in newer browsers]
// sum;
console.log(sum,fn); / / undefined ƒ fn () {}
function fn(){}
if(1! = =1) {function sum(){}}Copy the code

I see a long way to go, I will search up and down, refueling together, learn the front end!