Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

[js] 第63天 举例子说明javascript的变量声明提升和函数声明提升 #281

Open
haizhilin2013 opened this issue Jun 17, 2019 · 9 comments
Open

[js] 第63天 举例子说明javascript的变量声明提升和函数声明提升 #281

haizhilin2013 opened this issue Jun 17, 2019 · 9 comments
Labels
js JavaScript

Comments

@haizhilin2013
Copy link
Collaborator

第63天 举例子说明javascript的变量声明提升和函数声明提升
@xn213
Copy link

xn213 commented Jun 17, 2019 •
edited 

var getName = function(){
  console.log(4)
}

function getName() {
  console.log(5)
}

getName() // 4 函数声明优先级高于var声明,  故 4 覆盖了 5

@AnsonZnl
Copy link
Contributor

AnsonZnl commented Jun 18, 2019 •
edited

变量声明

console.log(a);// undefinde
var a= "hello world";
console.log(a);//  "hello world"

函数声明

f()
function f(){
    console.log('hello world');// "hello world"
}

变量声明只提升声明 不提升赋值操作，函数声明 函数体整体被提升。

getName();
var  getName = function(){
    console.log("小明");
}
function getName(){
    console.log("大明");
}
getName();

提升之后变成：

var getName;
function getName(){
    console.log("大明");
}
getName();//”大明“
getName= function(){
    console.log("小明");
}
getName();//"小明"

@wenyejie
Copy link 

var getName = function(){
  console.log(4)
}

function getName() {
  console.log(5)
}

getName() // 4 函数声明优先级高于var声明,  故 4 覆盖了 5

不是4的优先级是高于5, 而是5的优先级高于4,
5先声明, 但是后来它被4覆盖而已

@forever-z-133
Copy link

先声明函数名，再声明 var 变量名，然后按顺序从上到下赋值。

var a = 1;
function a() { }
console.log(a);  // 1

@yxkhaha
Copy link

yxkhaha commented Jun 18, 2019 

console.log(a);//undefined 变量a提升
var a = 10;

fn();//666 函数能在声明之前调用说明函数声明提升了
function fn() {
   console.log('666')
}

@haizhilin2013 haizhilin2013 added the js JavaScript label Jun 18, 2019
@Vi-jay
Copy link

Vi-jay commented Jul 31, 2019 

console.log(a);//a会被提升到作用域最前面声明 var a = undefined
var a = 1;
console.log(a);
var a = 1;

// 变量和函数都会被提升 函数优先
function a() {
  
}

@MrZ2019
Copy link

MrZ2019 commented Dec 31, 2020 

var getName = function(){
  console.log(4)
}

function getName() {
  console.log(5)
}

getName() // 4 函数声明优先级高于var声明,  故 4 覆盖了 5

@xiaoqiangz
Copy link

// 函数表达式 -- 匿名函数
var sum = function() {
console.log('sum2')
}
// 函数声明 --函数名 变量提升
function sum() {
console.log('sum')
}
sum()

var name = 'xxx'
function variable() {
  if (name == undefined) {
    var name = 'qqq'
    console.log(`hello ${name}`)
  } else {
    console.log(`hello ${name}`)
  }
}
variable()

@Frontendnightmare
Copy link

@AnsonZnl

变量声明

console.log(a);// undefinde
var a= "hello world";
console.log(a);//  "hello world"

函数声明

f()
function f(){
    console.log('hello world');// "hello world"
}

变量声明只提升声明 不提升赋值操作，函数声明 函数体整体被提升。

getName();
var  getName = function(){
    console.log("小明");
}
function getName(){
    console.log("大明");
}
getName();

提升之后变成：

var getName;
function getName(){
    console.log("大明");
}
getName();//”大明“
getName= function(){
    console.log("小明");
}
getName();//"小明"

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Assignees
No one assigned
Labels
js JavaScript
Projects
None yet
Milestone
No milestone
Development

No branches or pull requests
10 participants
@MrZ2019 @wenyejie @haizhilin2013 @xiaoqiangz @forever-z-133 @Vi-jay @AnsonZnl @yxkhaha @xn213 @Frontendnightmare