TypeScript is strongly typed, statically typed JavaScript

1. Classification of programming languages

As we all know, JavaScript is a weakly typed , dynamically typed programming language.
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First, let's explain these terms:

Dynamic type language : A language that does data type checking only during runtime (Runtime).
Static type language : Data type checking is performed during compilation (Compile). C/C++/Java is a typical representative of static language.
Strongly typed language : Mandatory type definition, to modify its type, an explicit type conversion must be performed.
Weakly typed language : A language in which data types can be ignored. (A variable can be assigned different types of values)

For the distinction between static type and dynamic type, there is a famous saying:

Static typing when possible, dynamic typing when needed

2. Give an example to illustrate the characteristics of JavaScript

As mentioned above JavaScript is a weakly typed , dynamically typed programming language. Here we do a demo, let's make fun of it.

// 在这里，定义一个简单的求和函数
function sum(x,y){
    
    
	return x + y
}

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These are the problems of weak typing . The most terrifying thing is that JavaScript is a dynamically typed language, and these errors must be found during runtime. ( The leaks are not repaired until the boat arrives in the middle of the river—too late )

At this time, senior people said that our JavaScript can also avoid the above problems:

// 这样做确实可以(只要你不怕麻烦)
function sum(x,y){
    
    
	 if(typeof(x) ==="number" && typeof(y)==="number"){
    
    
         return x + y
     }else{
    
    
         throw "invalid data"
     }
}

At this time, a classmate with strong type language experience made a speech - add data class to shape
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// 第一种方案：Uncaught SyntaxError: Unexpected token ':'
function sum(x:number,y:number){
    
    
	return x + y;
}
// 第二种方案：ncaught SyntaxError: Unexpected identifier 'x'
function sum(number x, number y){
    
    
	return x + y;
}

Isn't there a solution to give JavaScript developers a sense of security?

3. The power of TypeScript

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TypeScript has an unusual relationship with JavaScript. TypeScript provides all the functionality of JavaScript and adds a layer on top of it: TypeScript's type system .

Using TypeScript's type system, we can write code like this:

Type inference: By being aware of how JavaScript works, TypeScript can build a type system that accepts JavaScript code but has types. This type system eliminates the need for us to add extra characters to specify types explicitly .


// 创建变量并将其赋值给特定值时， TypeScript 将使用该值作为其类型。
const name:string = "BertKing"
// 类型推断
const name = "BertKing"

function sum(x:number,y:number):numbre{
    
    
	return x + y;
}

// 同理，TS具有类型推断能力，这里函数的返回值类型也可以省略
function sum(x:number,y:number){
    
    
	return x + y;
}

If we call sum(5,true), an error will be reported during compilation:
Use the TypeScript compiler at the terminal:
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Use VSCode:

In short, TypeScript will report obvious errors before the code is executed, and the rigor it brings can be effective avoid many mistakes. This is the so-called static type checking of TypeScript

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Strike while the iron is hot, let's get to know TypeScript Compiler (TSC) first