日常类型
在本章中,我们将介绍 JavaScript 代码中一些最常见的值类型,并解释在 TypeScript 中描述这些类型的相应方法。 这不是一个详尽的列表,未来的章节将描述更多命名和使用其他类型的方法。
类型也可以出现在更多的地方,而不仅仅是类型注释。 当我们了解类型本身时,我们还将了解可以引用这些类型以形成新结构的地方。
我们将首先回顾您在编写 JavaScript 或 TypeScript 代码时可能遇到的最基本和最常见的类型。 这些稍后将形成更复杂类型的核心构建块。
原语:string、number 和 boolean
JavaScript 有三个非常常用的 原语:string
、number
和 boolean
。 每个在 TypeScript 中都有对应的类型。 如您所料,如果您对这些类型的值使用 JavaScript typeof
运算符,这些名称与您看到的名称相同:
string
表示字符串值,如"Hello, world"
number
代表像42
这样的数字。JavaScript 对整数没有特殊的运行时值,因此没有等价于int
或float
- 一切都只是number
boolean
代表true
和false
这两个值
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数组
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any
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let obj: any = { x: 0 };
// None of the following lines of code will throw compiler errors.
// Using `any` disables all further type checking, and it is assumed
// you know the environment better than TypeScript.
obj.foo();
obj();
obj.bar = 100;
obj = "hello";
const n: number = obj;
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noImplicitAny
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变量的类型注释
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let myName: string = "Alice";
// ^^^^^^^^ Type annotation
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// No type annotation needed -- 'myName' inferred as type 'string'
let myName = "Alice";
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函数
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参数类型注解
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// Parameter type annotation
function greet(name: string) {
// ^^^^^^^^
console.log("Hello, " + name.toUpperCase() + "!!");
}
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declare function greet(name: string): void;
// Would be a runtime error if executed!
greet(42);
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返回类型注解
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function getFavoriteNumber(): number {
// ^^^^^^^^
return 26;
}
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匿名函数
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// No type annotations here, but TypeScript can spot the bug
const names = ["Alice", "Bob", "Eve"];
// Contextual typing for function
names.forEach(function (s) {
console.log(s.toUppercase());
});
// Contextual typing also applies to arrow functions
names.forEach((s) => {
console.log(s.toUppercase());
});
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对象类型
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// The parameter's type annotation is an object type
function printCoord(pt: { x: number; y: number }) {
// ^^^^^^^^^^^^^^^^^^^^^^^^
console.log("The coordinate's x value is " + pt.x);
console.log("The coordinate's y value is " + pt.y);
}
printCoord({ x: 3, y: 7 });
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可选属性
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function printName(obj: { first: string; last?: string }) {
// ...
}
// Both OK
printName({ first: "Bob" });
printName({ first: "Alice", last: "Alisson" });
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function printName(obj: { first: string; last?: string }) {
// Error - might crash if 'obj.last' wasn't provided!
console.log(obj.last.toUpperCase());
if (obj.last !== undefined) {
// OK
console.log(obj.last.toUpperCase());
}
// A safe alternative using modern JavaScript syntax:
console.log(obj.last?.toUpperCase());
}
联合类型
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定义联合类型
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function printId(id: number | string) {
console.log("Your ID is: " + id);
}
// OK
printId(101);
// OK
printId("202");
// Error
printId({ myID: 22342 });
使用联合类型
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function printId(id: number | string) {
console.log(id.toUpperCase());
}
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function printId(id: number | string) {
if (typeof id === "string") {
// In this branch, id is of type 'string'
console.log(id.toUpperCase());
} else {
// Here, id is of type 'number'
console.log(id);
}
}
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function welcomePeople(x: string[] | string) {
if (Array.isArray(x)) {
// Here: 'x' is 'string[]'
console.log("Hello, " + x.join(" and "));
} else {
// Here: 'x' is 'string'
console.log("Welcome lone traveler " + x);
}
}
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// Return type is inferred as number[] | string
function getFirstThree(x: number[] | string) {
return x.slice(0, 3);
}
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类型别名
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type Point = {
x: number;
y: number;
};
// Exactly the same as the earlier example
function printCoord(pt: Point) {
console.log("The coordinate's x value is " + pt.x);
console.log("The coordinate's y value is " + pt.y);
}
printCoord({ x: 100, y: 100 });
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type ID = number | string;
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declare function getInput(): string;
declare function sanitize(str: string): string;
type UserInputSanitizedString = string;
function sanitizeInput(str: string): UserInputSanitizedString {
return sanitize(str);
}
// Create a sanitized input
let userInput = sanitizeInput(getInput());
// Can still be re-assigned with a string though
userInput = "new input";
接口
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interface Point {
x: number;
y: number;
}
function printCoord(pt: Point) {
console.log("The coordinate's x value is " + pt.x);
console.log("The coordinate's y value is " + pt.y);
}
printCoord({ x: 100, y: 100 });
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类型别名和接口的区别
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`Interface` | `Type` |
---|---|
2he8PIdBmC9ARt/kueLdhw==
| esbX4BC4HzzN5vLWZnOlt33DTBrbxfwVs/4/UoGGphU=
|
6lvSMJml5+AGbaIYiG0x+zKd7m5HOkxhMclA6ctTmdU=
| E8TX5uAF8iI4rfhKuo+TnewIrOx6lyU2Ywsx7xTqV/A=
|
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- 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
tv6Vs5lkzpgl+lD7Loz7q1DVtiOcBbCVAtjWEFL+PvTofmVz49e/OAUaA7+T6dZAuLRWJmf9ZJno2UQidfE4JZKkb7VwAZgIiRiwSF44oUJTQgFMwi7Gq4ucFfNPrc+pb04oaOTQvyhfBUmVXXYDaZIyTDfHAY/aLXZ1v2ZBDkY0/ByJnE4PeZXc+BonCjmIEOXUdPxvWjB/yPjzq58F4wVcgzif7Ma7HCdLXyyEbAZM1lvhLz0S0gi3fgIbRTOlMWbMOo00cGvSu7JI64VR/NxYTH5BiiT+GR2Jt/kOm7hy4W8dA44MOXxWVnU7vTaNBUHEX3Y1+QQ6BDXUX/aq2g==
类型断言
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bWQB+mbS8RBosTCW1jRDqJgCNtWS/wT4Ki/Eomisc98D+vWFquHnApmoPTGiU0GaZZ4H9tdEvzwsM4UUE4bDVgrMoUYI66iQB0uZETl2fOQn1tBew7frJpfTNmrb4N+fH+XUUc8HhZkne/juYykt9HHYYzW+JxUALATqyEfY+UGzxQ4LtwuJ7y2KCXNFwlx/sQO/kv4qLjFpEa9iAnr8AShXk2htzmreVBXh/3X7Wm1gCKJPAE42KnsgYwAEnJvtsznxXR9jT2cRJHUxPh8BqsjVI6Mym0hABeckqr3hS9YMyf4MrBUqXeIT9j7L4gow
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const myCanvas = document.getElementById("main_canvas") as HTMLCanvasElement;
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const myCanvas = <HTMLCanvasElement>document.getElementById("main_canvas");
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const x = "hello" as number;
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declare const expr: any;
type T = { a: 1; b: 2; c: 3 };
const a = (expr as any) as T;
字面类型
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11kpE/drfWbsqE56B9A/qZJB51rq297ChFD64vREEriG6lKsM+Wm/GsPYM1D1cXjl/TEYycR+HFSf5oag17r43n7vECNJtcQ+xiXnhnoV74pdkA7uHqs1kAcT8YM4XLJGDHY/XAJb3USvB/IeKufQGEVCpP3y3ex75knll3SHmgqYgYHG0WUq5wZiJTmdBOPY3m7Iy+98Ly8vy2cpOpDAuh4jexnnHMzonrAX5UD+VdgsNpYwJDKV9/hNLN9LbMIWCRPTA60hXsTWmN3BkDnuMnJqC6FOHU1Hb6XTtGxBq4/HNExeUe3XF8iAGuZZXcnu5qdI4niu0q+fl4DxVfXI9afQ6uIYG+DCXWBv5smlHk=
let changingString = "Hello World";
changingString = "Olá Mundo";
// Because `changingString` can represent any possible string, that
// is how TypeScript describes it in the type system
changingString;
// ^?
const constantString = "Hello World";
// Because `constantString` can only represent 1 possible string, it
// has a literal type representation
constantString;
// ^?
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let x: "hello" = "hello";
// OK
x = "hello";
// ...
x = "howdy";
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function printText(s: string, alignment: "left" | "right" | "center") {
// ...
}
printText("Hello, world", "left");
printText("G'day, mate", "centre");
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function compare(a: string, b: string): -1 | 0 | 1 {
return a === b ? 0 : a > b ? 1 : -1;
}
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interface Options {
width: number;
}
function configure(x: Options | "auto") {
// ...
}
configure({ width: 100 });
configure("auto");
configure("automatic");
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字面推理
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declare const someCondition: boolean;
const obj = { counter: 0 };
if (someCondition) {
obj.counter = 1;
}
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bXWeUvJzE7tm79GvKjp2XTygMpcylfXDUEnHKNDPd1g=
declare function handleRequest(url: string, method: "GET" | "POST"): void;
const req = { url: "https://example.com", method: "GET" };
handleRequest(req.url, req.method);
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declare function handleRequest(url: string, method: "GET" | "POST"): void; // Change 1: const req = { url: "https://example.com", method: "GET" as "GET" }; // Change 2 handleRequest(req.url, req.method as "GET");
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declare function handleRequest(url: string, method: "GET" | "POST"): void; const req = { url: "https://example.com", method: "GET" } as const; handleRequest(req.url, req.method);
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null 和 undefined
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strictNullChecks 关闭
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strictNullChecks 开启
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function doSomething(x: string | null) {
if (x === null) {
// do nothing
} else {
console.log("Hello, " + x.toUpperCase());
}
}
非空断言运算符(后缀 !)
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function liveDangerously(x?: number | null) {
// No error
console.log(x!.toFixed());
}
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枚举
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不太常见的原语
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bigint
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// Creating a bigint via the BigInt function
const oneHundred: bigint = BigInt(100);
// Creating a BigInt via the literal syntax
const anotherHundred: bigint = 100n;
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symbol
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const firstName = Symbol("name");
const secondName = Symbol("name");
if (firstName === secondName) {
// Can't ever happen
}
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