JavaScript First Steps

In our first JavaScript module, we first answer some fundamental questions such as "what is JavaScript?", "what does it look like?", and "what can it do?", before moving on to taking you through your first practical experience of writing JavaScript. After that, we discuss some key building blocks in detail, such as variables, strings, numbers and arrays.

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We have put together a course that includes all the essential information you need to work towards your goal.

入门

先决条件

Before starting this module, you don't need any previous JavaScript knowledge, but you should have some familiarity with HTML and CSS. You are advised to work through the following modules before starting on JavaScript:

注意: If you are working on a computer/tablet/other device where you don't have the ability to create your own files, you could try out (most of) the code examples in an online coding program such as JSBin or Glitch .

指南

What is JavaScript?

Welcome to the MDN beginner's JavaScript course! In this first article we will look at JavaScript from a high level, answering questions such as "what is it?", and "what is it doing?", and making sure you are comfortable with JavaScript's purpose.

A first splash into JavaScript

Now you've learned something about the theory of JavaScript, and what you can do with it, we are going to give you a crash course in the basic features of JavaScript via a completely practical tutorial. Here you'll build up a simple "Guess the number" game, step by step.

What went wrong? Troubleshooting JavaScript

When you built up the "Guess the number" game in the previous article, you may have found that it didn't work. Never fear — this article aims to save you from tearing your hair out over such problems by providing you with some simple tips on how to find and fix errors in JavaScript programs.

Storing the information you need — Variables

After reading the last couple of articles you should now know what JavaScript is, what it can do for you, how you use it alongside other web technologies, and what its main features look like from a high level. In this article we will get down to the real basics, looking at how to work with the most basic building blocks of JavaScript — Variables.

Basic math in JavaScript — numbers and operators

At this point in the course we discuss maths in JavaScript — how we can combine operators and other features to successfully manipulate numbers to do our bidding.

Handling text — strings in JavaScript

Next we'll turn our attention to strings — this is what pieces of text are called in programming. In this article we'll look at all the common things that you really ought to know about strings when learning JavaScript, such as creating strings, escaping quotes in string, and joining them together.

Useful string methods

Now we've looked at the very basics of strings, let's move up a gear and start thinking about what useful operations we can do on strings with built-in methods, such as finding the length of a text string, joining and splitting strings, substituting one character in a string for another, and more.

数组

In the final article of this module, we'll look at arrays — a neat way of storing a list of data items under a single variable name. Here we look at why this is useful, then explore how to create an array, retrieve, add, and remove items stored in an array, and more besides.

Assessments

The following assessment will test your understanding of the JavaScript basics covered in the guides above.

Silly story generator

In this assessment you'll be tasked with taking some of the knowledge you've picked up in this module's articles and applying it to creating a fun app that generates random silly stories. Have fun!

另请参阅

学习 JavaScript

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  1. Complete beginners start here!
  2. Web 快速入门
    1. Getting started with the Web overview
    2. 安装基本软件
    3. What will your website look like?
    4. 处理文件
    5. HTML 基础
    6. CSS 基础
    7. JavaScript 基础
    8. 发布您的网站
    9. How the Web works
  3. HTML — Structuring the Web
  4. HTML 介绍
    1. Introduction to HTML overview
    2. Getting started with HTML
    3. What's in the head? Metadata in HTML
    4. HTML text fundamentals
    5. Creating hyperlinks
    6. Advanced text formatting
    7. Document and website structure
    8. Debugging HTML
    9. Assessment: Marking up a letter
    10. Assessment: Structuring a page of content
  5. 多媒体和嵌入
    1. Multimedia and embedding overview
    2. Images in HTML
    3. Video and audio content
    4. From object to iframe — other embedding technologies
    5. Adding vector graphics to the Web
    6. Responsive images
    7. Assessment: Mozilla splash page
  6. HTML 表格
    1. HTML tables overview
    2. HTML table basics
    3. HTML Table advanced features and accessibility
    4. Assessment: Structuring planet data
  7. CSS — Styling the Web
  8. CSS 第一步
    1. CSS first steps overview
    2. What is CSS?
    3. Getting started with CSS
    4. How CSS is structured
    5. How CSS works
    6. Using your new knowledge
  9. CSS 构建块
    1. CSS building blocks overview
    2. Cascade and inheritance
    3. CSS 选择器
    4. The box model
    5. Backgrounds and borders
    6. Handling different text directions
    7. Overflowing content
    8. Values and units
    9. Sizing items in CSS
    10. Images, media, and form elements
    11. Styling tables
    12. Debugging CSS
    13. Organizing your CSS
  10. 样式化文本
    1. Styling text overview
    2. Fundamental text and font styling
    3. Styling lists
    4. Styling links
    5. Web fonts
    6. Assessment: Typesetting a community school homepage
  11. CSS 布局
    1. CSS layout overview
    2. Introduction to CSS layout
    3. Normal Flow
    4. Flexbox
    5. Grids
    6. Floats
    7. 位置
    8. Multiple-column Layout
    9. Responsive design
    10. Beginner's guide to media queries
    11. Legacy Layout Methods
    12. Supporting Older Browsers
    13. Fundamental Layout Comprehension
  12. JavaScript — Dynamic client-side scripting
  13. JavaScript 第一步
    1. JavaScript first steps overview
    2. What is JavaScript?
    3. A first splash into JavaScript
    4. What went wrong? Troubleshooting JavaScript
    5. Storing the information you need — Variables
    6. Basic math in JavaScript — Numbers and operators
    7. Handling text — Strings in JavaScript
    8. Useful string methods
    9. 数组
    10. Assessment: Silly story generator
  14. JavaScript 构建块
    1. JavaScript building blocks overview
    2. Making decisions in your code — Conditionals
    3. Looping code
    4. Functions — Reusable blocks of code
    5. Build your own function
    6. Function return values
    7. 事件介绍
    8. Assessment: Image gallery
  15. 引入 JavaScript 对象
    1. Introducing JavaScript objects overview
    2. Object basics
    3. 对象原型
    4. Object-oriented programming concepts
    5. Classes in JavaScript
    6. Working with JSON data
    7. Object building practice
    8. Assessment: Adding features to our bouncing balls demo
  16. 异步 JavaScript
    1. Asynchronous JavaScript overview
    2. General asynchronous programming concepts
    3. Introducing asynchronous JavaScript
    4. Cooperative asynchronous Java​Script: Timeouts and intervals
    5. Graceful asynchronous programming with Promises
    6. Making asynchronous programming easier with async and await
    7. Choosing the right approach
  17. 客户端侧 Web API
    1. 客户端侧 Web API
    2. Introduction to web APIs
    3. Manipulating documents
    4. Fetching data from the server
    5. Third party APIs
    6. Drawing graphics
    7. Video and audio APIs
    8. Client-side storage
  18. Web forms — Working with user data
  19. Core forms learning pathway
    1. Web forms overview
    2. Your first form
    3. How to structure a web form
    4. Basic native form controls
    5. The HTML5 input types
    6. Other form controls
    7. Styling web forms
    8. Advanced form styling
    9. UI pseudo-classes
    10. Client-side form validation
    11. Sending form data
  20. Advanced forms articles
    1. How to build custom form controls
    2. Sending forms through JavaScript
    3. CSS property compatibility table for form controls
  21. Accessibility — Make the web usable by everyone
  22. Accessibility guides
    1. Accessibility overview
    2. What is accessibility?
    3. HTML: A good basis for accessibility
    4. CSS and JavaScript accessibility best practices
    5. WAI-ARIA basics
    6. Accessible multimedia
    7. Mobile accessibility
  23. Accessibility assessment
    1. Assessment: Accessibility troubleshooting
  24. Tools and testing
  25. Client-side web development tools
    1. Client-side web development tools index
    2. Client-side tooling overview
    3. Command line crash course
    4. Package management basics
    5. Introducing a complete toolchain
    6. Deploying our app
  26. Introduction to client-side frameworks
    1. Client-side frameworks overview
    2. Framework main features
  27. React
    1. Getting started with React
    2. Beginning our React todo list
    3. Componentizing our React app
    4. React interactivity: Events and state
    5. React interactivity: Editing, filtering, conditional rendering
    6. Accessibility in React
    7. React resources
  28. Ember
    1. Getting started with Ember
    2. Ember app structure and componentization
    3. Ember interactivity: Events, classes and state
    4. Ember Interactivity: Footer functionality, conditional rendering
    5. Routing in Ember
    6. Ember resources and troubleshooting
  29. Vue
    1. Getting started with Vue
    2. Creating our first Vue component
    3. Rendering a list of Vue components
    4. Adding a new todo form: Vue events, methods, and models
    5. Styling Vue components with CSS
    6. Using Vue computed properties
    7. Vue conditional rendering: editing existing todos
    8. Focus management with Vue refs
    9. Vue resources
  30. Svelte
    1. Getting started with Svelte
    2. Starting our Svelte Todo list app
    3. Dynamic behavior in Svelte: working with variables and props
    4. Componentizing our Svelte app
    5. Advanced Svelte: Reactivity, lifecycle, accessibility
    6. Working with Svelte stores
    7. TypeScript support in Svelte
    8. Deployment and next steps
  31. Angular
    1. Getting started with Angular
    2. Beginning our Angular todo list app
    3. Styling our Angular app
    4. Creating an item component
    5. Filtering our to-do items
    6. Building Angular applications and further resources
  32. Git and GitHub
    1. Git and GitHub overview
    2. Hello World
    3. Git Handbook
    4. Forking Projects
    5. About pull requests
    6. Mastering Issues
  33. Cross browser testing
    1. Cross browser testing overview
    2. Introduction to cross browser testing
    3. Strategies for carrying out testing
    4. Handling common HTML and CSS problems
    5. Handling common JavaScript problems
    6. Handling common accessibility problems
    7. Implementing feature detection
    8. Introduction to automated testing
    9. Setting up your own test automation environment
  34. Server-side website programming
  35. 第一步
    1. First steps overview
    2. Introduction to the server-side
    3. Client-Server overview
    4. Server-side web frameworks
    5. Website security
  36. Django Web 框架 (Python)
    1. Django web framework (Python) overview
    2. 介绍
    3. 设置开发环境
    4. Tutorial: The Local Library website
    5. Tutorial Part 2: Creating a skeleton website
    6. Tutorial Part 3: Using models
    7. Tutorial Part 4: Django admin site
    8. Tutorial Part 5: Creating our home page
    9. Tutorial Part 6: Generic list and detail views
    10. Tutorial Part 7: Sessions framework
    11. Tutorial Part 8: User authentication and permissions
    12. Tutorial Part 9: Working with forms
    13. Tutorial Part 10: Testing a Django web application
    14. Tutorial Part 11: Deploying Django to production
    15. Web application security
    16. Assessment: DIY mini blog
  37. Express Web Framework (node.js/JavaScript)
    1. Express Web Framework (Node.js/JavaScript) overview
    2. Express/Node introduction
    3. Setting up a Node (Express) development environment
    4. Express tutorial: The Local Library website
    5. Express Tutorial Part 2: Creating a skeleton website
    6. Express Tutorial Part 3: Using a database (with Mongoose)
    7. Express Tutorial Part 4: Routes and controllers
    8. Express Tutorial Part 5: Displaying library data
    9. Express Tutorial Part 6: Working with forms
    10. Express Tutorial Part 7: Deploying to production
  38. Further resources
  39. Common questions
    1. HTML questions
    2. CSS questions
    3. JavaScript questions
    4. Web mechanics
    5. Tools and setup
    6. Design and accessibility