javascript IIFE in depth

function type

函数表达式


x = function (){
    console.log(x); 
}
ƒ (){
    console.log(x); 
}

x;
ƒ (){
    console.log(x); 
}

x();
ƒ (){
    console.log(x); 
}

window.x;
ƒ (){
    console.log(x); 
}

x = function x(){
    console.log(x); 
}
ƒ x(){
    console.log(x); 
}

x();
ƒ x(){
    console.log(x); 
}

window.x;
ƒ x(){
    console.log(x); 
}

函数声明


function x(){
    console.log(x); 
}

x();
ƒ x(){
    console.log(x); 
}

window.x
ƒ x(){
    console.log(x); 
}

考察知识点

closure
IIFE
hoisting
scope
function declaration / function expression
named function / anonymous function

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions

closure

https://javascript.info/closure

js var hoisting

function
var

demo

https://muyiy.cn/question/js/33.html

// 下面的代码打印什么内容，为什么？

var b = 10;
(function b(){
    b = 20;
    console.log(b); 
})();

var b = 10;
(function b(){
    b = 20;
    console.log(b); 
    console.log(window.b); 
})();


ƒ b(){
    b = 20;
    console.log(b); 
    console.log(window.b); 
}
// 10

函数表达式的函数名是常量，无法二次赋值(在正常模式下静默失效，在严格模式下报错)

非匿名自执行函数，函数名只读

`'use strict';`

var b = 10;
(function b(){
    'use strict';
    b = 20;
    console.log(b); 
    console.log(window.b); 
})();

//  Uncaught TypeError: Assignment to constant variable.
    at b (<anonymous>:4:7)
    at <anonymous>:7:3

https://github.com/Advanced-Frontend/Daily-Interview-Question/issues/48#issuecomment-615547271