The purpose of the Typescript

Typescript is a solution to the problem of dynamic typing in Javascript, which is inconvenient to read and a performance penalty for browser parsing

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variable

Basic types of

Common basic types include Boolean, Number, String, undefined, null, and so on

  1. Boolean, Number, String

    let count: number = 0.05;
let numResult = count.toFixed(1);
// Numeric types can use numeric type methods

console.log(`numResult`, numResult); / / 0.5

let myName: string = 'sheldonWong';
let strResult = myName.slice(0.7);
// String type you can use string type methods
console.log(`strResult`, strResult); //sheldon

let isUsed: boolean = true;
let boolResult = isUsed.valueOf();
// Boolean types can use Boolean type methods
console.log(`boolResult`, boolResult); //true

// An optional type, which can be a number or a string
let num_or_Str: string | number = 2;
let num_or_Str2: string | number = 'sheldon';
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  2. Undefined, null,

    let u: undefined = undefined;
let n: null = null;
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  3. Enum Enum type Usage scenario: Used to identify status

    
enum STATUS {
  REJECT,
  PENDING,
  RESOLVE
}
/* STATUS.REJECT ===0 STATUS.PENDING ===1 STATUS.RESOLVE ===2 */

enum STATUS {
  REJECT=-1,
  PENDING,
  RESOLVE
}
REJECT ===-1 // Changing a value changes the following value: status.pending ===0 status.resolve ===1 */
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    Note that:

    1. Naming should avoid keywords
    2. You can also set it value by value if necessary

The compound type

  1. Object

    let person1: { name: string, age: number } = { name: 'sheldon'.age: 25 };
let person2: { name: string, age: number } = { name: 'Tom'.age: 21 };
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    If a variable of the same type is needed, alias names can be used instead of duplicate objects

    type Person = {
	name: string,
	age: number,
};
let person1: Person = { name: 'sheldon'.age: 25 };
let person2: Person = { name: 'foo'.age: 26 };
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  2. Array

    let strArray: string[] = ['s'.'h'.'e'.'l'.'d'.'o'.'n'];
let numArray: number[] = [1.2.3.4.5.6.7];
let list: Array<number> = [1.2.3.4.5.6.7];

// Store objects in an Array
let ObjArray3: { name: string, age: number }[] = [{ name: 'sheldon'.age: 25 }];
/ / is equivalent to
let ObjArray3: Person[] = [{ name: 'sheldon'.age: 25 }];
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  3. Turple (New data type for Ts)

    let x: [string, number] = ['hey'.10];
// Tuples specify positions and lengths, otherwise the same as arrays
// A tuple is a fixed array

let y: (string | number)[] = [25.'sheldon'];
// Different declarations lead to different results
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