嗨！我是前端小M~~
作用域
for (let i = 0; i < 3; i++) { for (var i = 0; i < 3; i++) {
console.log(i); // 0 1 2 console.log(i); //0 1 2
} }
console.log(i); // i is not defined console.log(i); //3
console.log(a); //Cannot access ‘a‘ before initialization console.log(a); let a = 5; var a = 5;
let test = 5; function test(){
function test(){ console.log(`heihei`);
console.log(`heihei`); }
} let test = 5;
console.log(test); //5 ====变量提升=====> console.log(test); //5
console.log(typeof test);//num console.log(typeof test);//num
test(); //未声明 5();//???
let b = 2; //被a赋值为1
let fn1 = function (){
let a = 1; //局部
b=a; //局部变量赋值给全局
}
let fn2 = function (){
console.log(b); //1
}
fn1();
fn2();
let fn1 = function () {
let a = 1;
fn2(a);
}
let fn2 = function (x) {
console.log(x); //1
}
fn1();
let fn1 = function () {
let a = 1;
return a; //1
}
let result = fn1();//1
let fn2 = function () {
console.log(result);//1
}
fn2();
原文：https://www.cnblogs.com/trail0226/p/14128988.html