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TypeScript 代码示例
一：类型映射(Mapped Types)
const data = {
value: 123,
text: “text”,
subData: {
value: false}
};
type Data = typeof data;
// type Data = {
// value: number;
// text: string;
// subData: {
// value: boolean;
// }
const data = [“text 1”, “text 2”] as const;
type Data = typeof data[number]; // “text 1” | “text 2”
const locales = [
{
locale: "se",
language: "Swedish"},
{
locale: "en",
language: "English"}
] as const;
type Locale = typeof localesnumber; // “se” | “en”
const currencySymbols = {
GBP: “£”,
USD: “$”,
EUR: “€”
};
type CurrencySymbol = keyof typeof currencySymbols; // “GBP” | “USD” | “EUR”
二：Keyof 与泛型（Generics）
interface HasPhoneNumber {
name: string;
phone: number;
}
interface HasEmail {
name: string;
email: string;
}
interface CommunicationMethods {
email: HasEmail;
phone: HasPhoneNumber;
fax: {fax: number};
}
function contact<K extends keyof CommunicationMethods>(
method: K,
contact: CommunicationMethods[K] // turning key into value – a mapped type
) {
//…
}
contact(“email”, { name: “foo”, email: “mike@example.com”});
contact(“phone”, { name: “foo”, phone: 3213332222});
contact(“fax”, { fax: 1231});
三：const 断言
数字转为数字字面量类型
// Type ’10’
let x = 10 as const;
四：高阶函数 (Higher Order Function)
function logDuration<T extends (…args: any[]) => any>(func: T) {
const funcName = func.name;
// Return a new function that tracks how long the original took
return (…args: Parameters): ReturnType => {
console.time(funcName);
const results = func(...args);
console.timeEnd(funcName);
return results;};
}
function addNumbers(a: number, b: number): number {
return a + b;
}
// Hover over is addNumbersWithLogging: (a: number, b: number) => number
const addNumbersWithLogging = logDuration(addNumbers);
addNumbersWithLogging(5, 3);
五：工厂
工厂模式的存在是为了解耦 (废话，任何设计模式都为了解耦) 调用者和被调用模块间的关系。比如当下零碎使用的是 sql server，为了未来切换其余 db server 时不至于每个调用的地方都修改，就要使用工厂来创建 sql server 模块。
而后，以集体理解，ioc 可能无效地替换工厂。不论如何，先记录一下代码的实例。
class Hero {
constructor(public point: [number, number]) {}
}
const entities = [];
const entityFactory = <
T extends {
new (...args: any[]): any;}
(
classToCreate: T,
numberOf: number,
…args: ConstructorParameters
): InstanceType[] =>
[…Array(numberOf)].map(() => new classToCreate(…args));
entities.push(…entityFactory(Hero, 10, [12, 10]));
六：never 的使用
利用 never 与其余任何类型都不兼容的个性(除了 never 外，没有值可能赋给 never，包含 any)，以控制代码在编译时就报错。
interface Square {
kind: “square”;
size: number;
}
interface Rectangle {
kind: “rectangle”;
width: number;
height: number;
}
interface Circle {
kind: “circle”;
radius: number;
}
interface Triangle {
kind: “triangle”;
whatever: number;
}
type Shape = Square | Rectangle | Circle | Triangle;
function assertNever(x: never): never {
throw new Error(“Unexpected object: ” + x);
}
function area(s: Shape) {
switch (s.kind) {
case "square":
return s.size * s.size;
case "rectangle":
return s.height * s.width;
case "circle":
return Math.PI * s.radius ** 2;
default:
return assertNever(s); // Error
// Argument of type 'Triangle' not assignable to param of type 'never'}
}
七：断言(Assert)
function assert(condition: any, msg?: string): asserts condition {
if (!condition) {
throw new AssertionError(msg);}
}
function yell(str) {
assert(typeof str === “string”);
return str.toUppercase();
// ~~~
// error: Property ‘toUppercase’ does not exist on type ‘string’.
// Did you mean ‘toUpperCase’?
