Comments (1)
在JavaScript中,变量和函数声明会在代码执行之前被提升到其所在作用域的顶部。但是,这种提升只涉及到声明部分,而不包括赋值。
让我们针对你的例子重新解释:
console.log(a); // 输出:function a() {}
var a = 1;
console.log(a); // 输出:1
function a() {}
console.log(a); // 输出:1
-
变量和函数声明提升:
- 变量
a
和函数a
都被提升到作用域的顶部。在提升阶段,函数声明会覆盖变量声明。
- 变量
-
代码执行:
-
第一个
console.log(a);
遇到的是函数声明,因为在提升阶段,函数声明覆盖了变量声明。所以输出function a() {}
。 -
var a = 1;
这一行的赋值部分不会影响提升阶段的输出。在提升阶段,a
被视为函数。 -
第二个
console.log(a);
输出的是变量a
的值,因为在这一行之前,变量a
已经被重新赋值为1
。所以输出1
。 -
第三个
console.log(a);
输出的仍然是变量a
的值,即1
。
-
总体来说,提升阶段会将声明提升到作用域的顶部,函数声明会覆盖变量声明,但赋值部分不会在提升阶段执行。
from fe-interview.
Related Issues (20)
- nuxt有哪些特性?为什么要用nuxt做服务端渲染?它解决了什么问题? HOT 1
- CSS Sprites(雪碧图)原理及其优缺点 HOT 1
- 图片懒加载原理及如何实现 HOT 1
- JS获取url参数的方法 HOT 1
- 手写实现一个合乎规范的Promise HOT 1
- requestAnimationFrame原理及兼容性封装 HOT 1
- 用过HappyPack吗?HappyPack有什么优点? HOT 2
- eslint忽略全局变量的方法 HOT 1
- webpack配置路径别名 HOT 1
- webpack添加路径别名后,vscode不能智能提示,如何解决? HOT 1
- 如何只用两行代码实现判断js中所有数据类型 HOT 1
- nrm和nvm HOT 1
- 不用window.open打开新窗口 HOT 1
- js中精度问题及解决方案 HOT 2
- webpack之less-loader、css-loader、style-loader执行顺序 HOT 1
- js实现普通数组去重&json数组去重 HOT 1
- 常见的js模板引擎
- js原生实现拷贝到剪贴板 HOT 1
- iframe内嵌网页未知高度如何自适应 HOT 1
Recommend Projects
-
React
A declarative, efficient, and flexible JavaScript library for building user interfaces.
-
Vue.js
🖖 Vue.js is a progressive, incrementally-adoptable JavaScript framework for building UI on the web.
-
Typescript
TypeScript is a superset of JavaScript that compiles to clean JavaScript output.
-
TensorFlow
An Open Source Machine Learning Framework for Everyone
-
Django
The Web framework for perfectionists with deadlines.
-
Laravel
A PHP framework for web artisans
-
D3
Bring data to life with SVG, Canvas and HTML. 📊📈🎉
-
Recommend Topics
-
javascript
JavaScript (JS) is a lightweight interpreted programming language with first-class functions.
-
web
Some thing interesting about web. New door for the world.
-
server
A server is a program made to process requests and deliver data to clients.
-
Machine learning
Machine learning is a way of modeling and interpreting data that allows a piece of software to respond intelligently.
-
Visualization
Some thing interesting about visualization, use data art
-
Game
Some thing interesting about game, make everyone happy.
Recommend Org
-
Facebook
We are working to build community through open source technology. NB: members must have two-factor auth.
-
Microsoft
Open source projects and samples from Microsoft.
-
Google
Google ❤️ Open Source for everyone.
-
Alibaba
Alibaba Open Source for everyone
-
D3
Data-Driven Documents codes.
-
Tencent
China tencent open source team.
from fe-interview.