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typescript学习总结 #48

Open xiaokeqi opened 4 years ago

xiaokeqi commented 4 years ago

介绍

Typescript 对代码进行了静态分析，排除一些类型错误,其是js的超集。TypeScript使用的是结构性类型系统。 当我们比较两种不同的类型时，并不在乎它们从何处而来，如果所有成员的类型都是兼容的，我们就认为它们的类型是兼容的。因此在使用时，只要牢记这条准则，就能帮组我们排除大多编译不通过问题！

基础类型

类型断言

类型断言，可以理解为类型转换，但js中的类型转换是在运行时进行转换的，而类型断言是ts在编译时进行转换的，它是一种人为的“主观意愿”的转换，告诉编译器它不应该报错，其是此类型的

看个例子

const foo = {};
foo.bar = 123; // Error: 'bar' 属性不存在于 ‘{}’
foo.bas = 'hello'; // Error: 'bas' 属性不存在于 '{}'

这个经过ts编译时，会报Error

而经过类型断言后，

interface Foo {
  bar: number;
  bas: string;
}

const foo = {} as Foo;
foo.bar = 123;
foo.bas = 'hello';

编译器会强制把{},解析为Foo类型，即将{}转换为了Foo类型，从而绕过了编译器的编译机制。不再报错

接口

1、属性接口

保证两个类型内部结构兼容，则为实现接口，如

interface Person {
    name: string;
    age: number;
    hobby?: string;
    readonly x: number;
}
function greeter(person: Person) {
    return "Hello, " + person.name + ", i am " + person.age + "years old";
}
let user = { name: "Jane", age: 23, sex: 'male',x:5 };
document.body.innerHTML = greeter(user);

注：

2、函数类型接口

举例如下：

interface SearchFunc {
  //  参数列表定义                        函数返回返回值
  (source: string, subString: string): boolean;
}

其就像是一个只有参数列表和返回值类型的函数定义，其中对其参数名称不做检查，只检查其类型，即

参数类型一致、函数返回值一致。即为实现了函数类型接口。

如

let mySearch: SearchFunc;
mySearch = function(src: string, sub: string): boolean {
  let result = src.search(sub);
  return result > -1;
}

3、可索引的类型接口

用于数组类如a[10]或对象类如ageMap["daniel"]，具体如下

interface NumberDictionary {
  [index: string]: number;
  length: number;    // 可以，length是number类型
}

let myDictionary: NumberDictionary;
myDictionary = {
    age: 29,
    length: 7
};
interface NumberDictionary {
  [index: number]: string;
}
let myArray: NumberDictionary = ['xiaoqi', 'dandan'];

4、类类型接口

强制类符合接口规则

interface ClockInterface {
    currentTime: Date;
    setTime(d: Date);
}
class Clock implements ClockInterface {
    currentTime: Date;
    setTime(d: Date) {
        this.currentTime = d;
    }
    constructor(h: number, m: number) { }
}

5、继承接口

如下：

interface Shape {
    color: string;
}
interface PenStroke {
    penWidth: number;
}
interface Square extends Shape, PenStroke {
    sideLength: number;
}
let square = <Square>{};
square.color = "blue";
square.sideLength = 10;
square.penWidth = 5.0;

6、混合类型接口

有时我们希望一个对象，既可以当做对象又可以当做函数、并带有额外属性，此样子的接口定义如下：

interface Counter {
    (start: number): string;
    interval: number;
    reset(): void;
}
function getCounter(): Counter {
    let counter = <Counter>function (start: number) { };
    counter.interval = 123;
    counter.reset = function () { };
    return counter;
}
let c = getCounter();
c(10);
c.reset();
c.interval = 5.0;

7、接口继承类

当接口继承了一个类类型时，它会继承类的成员但不包括其实现。 就好像接口声明了所有类中存在的成员，但并没有提供具体实现一样。 接口同样会继承到类的private和protected成员。 这意味着当你创建了一个接口继承了一个拥有私有或受保护的成员的类时，这个接口类型只能被这个类或其子类所实现（implement）。

class Control {
    private state: any;
}
interface SelectableControl extends Control {
    select(): void;
}
class Button extends Control implements SelectableControl {
    select() { }
}
class TextBox extends Control {
    select() { }
}
// 错误：“Image”类型缺少“state”属性。
class Image implements SelectableControl {
    select() { }
}
class Location {
}

类

1、基本用法

class Animal {
    name: string;
    constructor(theName: string) { this.name = theName; }
    move(distanceInMeters: number = 0) {
        console.log(`${this.name} moved ${distanceInMeters}m.`);
    }
}
class Snake extends Animal {
    constructor(name: string) { super(name); }
    move(distanceInMeters = 5) {
        console.log("Slithering...");
        super.move(distanceInMeters);
    }
}
class Horse extends Animal {
    constructor(name: string) { super(name); }
    move(distanceInMeters = 45) {
        console.log("Galloping...");
        super.move(distanceInMeters);
    }
}
let sam = new Snake("Sammy the Python");
let tom: Animal = new Horse("Tommy the Palomino");
sam.move();
tom.move(34);

经过tsc编译后的代码如下：

var __extends = (this && this.__extends) || (function () {
    var extendStatics = function (d, b) {
        extendStatics = Object.setPrototypeOf ||
            ({ __proto__: [] } instanceof Array && function (d, b) { d.__proto__ = b; }) ||
            function (d, b) { for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p]; };
        return extendStatics(d, b);
    };
    return function (d, b) {
        extendStatics(d, b);
        function __() { this.constructor = d; }
        d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
    };
})();
var Animal = /** @class */ (function () {
    function Animal(theName) {
        this.name = theName;
    }
    Animal.prototype.move = function (distanceInMeters) {
        if (distanceInMeters === void 0) { distanceInMeters = 0; }
        console.log(this.name + " moved " + distanceInMeters + "m.");
    };
    return Animal;
}());
var Snake = /** @class */ (function (_super) {
    __extends(Snake, _super);
    function Snake(name) {
        return _super.call(this, name) || this;
    }
    Snake.prototype.move = function (distanceInMeters) {
        if (distanceInMeters === void 0) { distanceInMeters = 5; }
        console.log("Slithering...");
        _super.prototype.move.call(this, distanceInMeters);
    };
    return Snake;
}(Animal));
var Horse = /** @class */ (function (_super) {
    __extends(Horse, _super);
    function Horse(name) {
        return _super.call(this, name) || this;
    }
    Horse.prototype.move = function (distanceInMeters) {
        if (distanceInMeters === void 0) { distanceInMeters = 45; }
        console.log("Galloping...");
        _super.prototype.move.call(this, distanceInMeters);
    };
    return Horse;
}(Animal));
var sam = new Snake("Sammy the Python");
var tom = new Horse("Tommy the Palomino");
sam.move();
tom.move(34);

2、修饰符

3、存取器

TypeScript支持通过getters/setters来截取对对象成员的访问。 它能帮助你有效的控制对对象成员的访问。

let passcode = "secret passcode";
class Employee {
    private _fullName: string;
    get fullName(): string {
        return this._fullName;
    }
    set fullName(newName: string) {
        if (passcode && passcode == "secret passcode") {
            this._fullName = newName;
        }
        else {
            console.log("Error: Unauthorized update of employee!");
        }
    }
}
let employee = new Employee();
employee.fullName = "Bob Smith";
if (employee.fullName) {
    alert(employee.fullName);
}

tsc转换后为

var passcode = "secret passcode";
var Employee = /** @class */ (function () {
    function Employee() {
    }
    Object.defineProperty(Employee.prototype, "fullName", {
        get: function () {
            return this._fullName;
        },
        set: function (newName) {
            if (passcode && passcode == "secret passcode") {
                this._fullName = newName;
            }
            else {
                console.log("Error: Unauthorized update of employee!");
            }
        },
        enumerable: true,
        configurable: true
    });
    return Employee;
}());
var employee = new Employee();
employee.fullName = "Bob Smith";
if (employee.fullName) {
    alert(employee.fullName);
}

4、静态属性

class Grid {
    static origin = {x: 0, y: 0};
    calculateDistanceFromOrigin(point: {x: number; y: number;}) {
        let xDist = (point.x - Grid.origin.x);
        let yDist = (point.y - Grid.origin.y);
        return Math.sqrt(xDist * xDist + yDist * yDist) / this.scale;
    }
    constructor (public scale: number) { }
}
let grid1 = new Grid(1.0);  // 1x scale
let grid2 = new Grid(5.0);  // 5x scale
console.log(grid1.calculateDistanceFromOrigin({x: 10, y: 10}));
console.log(grid2.calculateDistanceFromOrigin({x: 10, y: 10}));

tsc编译后

var Grid = /** @class */ (function () {
    function Grid(scale) {
        this.scale = scale;
    }
    Grid.prototype.calculateDistanceFromOrigin = function (point) {
        var xDist = (point.x - Grid.origin.x);
        var yDist = (point.y - Grid.origin.y);
        return Math.sqrt(xDist * xDist + yDist * yDist) / this.scale;
    };
    Grid.origin = { x: 0, y: 0 };
    return Grid;
}());
var grid1 = new Grid(1.0); // 1x scale
var grid2 = new Grid(5.0); // 5x scale
console.log(grid1.calculateDistanceFromOrigin({ x: 10, y: 10 }));
console.log(grid2.calculateDistanceFromOrigin({ x: 10, y: 10 }));

5、抽象类

抽象类做为其它派生类的基类使用。 它们一般不会直接被实例化。 不同于接口，抽象类可以包含成员的实现细节。 abstract关键字是用于定义抽象类和在抽象类内部定义抽象方法。

抽象类中的抽象方法不包含具体实现并且必须在派生类中实现。 抽象方法的语法与接口方法相似。 两者都是定义方法签名但不包含方法体。 然而，抽象方法必须包含 abstract关键字并且可以包含访问修饰符。

abstract class Department {
    constructor(public name: string) {
    }
    printName(): void {
        console.log('Department name: ' + this.name);
    }
    abstract printMeeting(): void; // 必须在派生类中实现
}
class AccountingDepartment extends Department {
    constructor() {
        super('Accounting and Auditing'); // 在派生类的构造函数中必须调用 super()
    }
    printMeeting(): void {
        console.log('The Accounting Department meets each Monday at 10am.');
    }
    generateReports(): void {
        console.log('Generating accounting reports...');
    }
}
let department: Department; // 允许创建一个对抽象类型的引用
department = new Department(); // 错误: 不能创建一个抽象类的实例
department = new AccountingDepartment(); // 允许对一个抽象子类进行实例化和赋值
department.printName();
department.printMeeting();
department.generateReports(); // 错误: 方法在声明的抽象类中不存在

函数