What is the difference between typescript and javascript

First let’s take a look at the definitions of the two:

What is javascript?

JavaScript is a lightweight interpreted scripting language that does not require compilation. It can be embedded into HTML pages and executed on the browser side. It can realize rich interactive functions on the browser side and bring smoothness to users. Diverse user experience.

What is typescript?

TypeScript code is saved in the ts file. After the ts file is compiled, a js file will be generated. Any valid JavaScript code can be directly compiled as TypeScript code, but the compiled code is the same as the original JavaScript code. After TypeScript code is compiled, it will be converted into the corresponding JavaScript code.

Then let’s take a look at the content comparison between the two:

1. TypeScript introduces the concept of “class” that is not found in JavaScript;

Although ES6 already supports classes, TypeScript and ES6 classes are still not exactly the same. ts code can declare the type of variables through type annotations.

2. Data in TypeScript requires clear types, which JavaScript does not require;

3. TypeScript provides compile-time static type checking through type annotations

let str: string;//ts代码
let str;//编译生成的js代码

Passed The comparison can clearly see that in ts code, ": type" can be added when declaring a variable to describe the type of the variable, that is, type annotation.

4. TypeScript extends the JavaScript object model from the core language aspect and the modeling of class concepts;

5. JavaScript code can work with TypeScript without any modification. At the same time, you can use the compiler to convert TypeScript code into JavaScript;

6. TypeScript provides default parameter values ​​for functions;

In TypeScript functions, we can provide type annotations for each parameter. , and can also provide return type annotations (":type" after the parameter list) for functions, and TypeScript can add a [? to the right of the parameter name. 】Indicates optional parameters;

7. TypeScript introduces the concept of modules, which can encapsulate declarations, data, functions and classes in modules.

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