Notice that we passedinstead ofto theutility type. I wrotea bookin which I share everything I know about how to become a better, more efficient programmer. You can use the search field on myHome Pageto filter through all of my articles. ...
:number;// Optional property}// Declare the 'employees' array of type Employeeletemployees:Employee[];// Initialize the array with Employee objectsemployees=[{name:"John",position:"Manager",age:30},{name:"Jane",position:"Developer"},// 'age' is optional here{name...
functionadd(x:number|string, y:number|string){if(typeofx ==='number'&&typeofy ==='number') {returnx + y; }if(typeofx ==='string'&&typeofy ==='string') {returnx.concat(y); }thrownewError('Parameters must be numbers or strings'); }console.log(add('one','two'));//...
array /** * 数组的类型声明: * 类型[] * Array<类型> */ // string[] 表示字符串数组 let e: string[] e = ['a', 'b', 'c'] // number[] 表示数值数组 let f: number[] let g: Array<number> g = [1, 2, 3] 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14....
let strings: string[] = pluck(person, [‘name’]); // ok, string[] 编译器会检查name是否真的是Person的一个属性。 本例还引入了几个新的类型操作符。 首先是keyof T,索引类型查询操作符。 对于任何类型T,keyof T的结果为T上已知的公共属性名的联合。 例如: let personProps: keyof Person; // ‘...
* - returns strings * - can be passed in booleans */function*counter:Generator<number,string,boolean>{ leti=0; while(true){ if(yieldi++){ break; } } return"done!";}variter=counter;varcurr=iter.nextwhile(!curr.done){ console.log(curr.value); ...
declare global { namespace JSX { interface Element extends React.ReactElement<any, any>{ } } } 可以看到,JSX.Element是ReactElement的子类型,它没有增加属性,两者是等价的。也就是说两种类型的变量可以相互赋值。 JSX.Element 可以通过执行 React.createElement 或是转译 JSX 获得: ...
functionuppercaseStrings(x:string|number){if(typeofx==="string"){// TypeScript在这里知道'x'是一个'string'returnx.toUpperCase();}} 一个常见的痛点是,我们在闭包函数里是感知不到这些被收窄后的类型的。 代码语言:javascript 复制 functiongetUrls(url:string|URL,names:string[]){if(typeofurl==="...
// node_modules/dep/index.d.ts export declare function doSomething(): void; // index.ts // Okay if "dep" is a CommonJS module, but fails if // it's an ECMAScript module - even in bundlers! import dep from "dep"; dep.doSomething(); In practice, this didn’t come up very...
declare function uniqueId(): number; const ID = Symbol('ID'); interface Person { [ID]: number; name: string; age: number; } // Allows changing the person data as long as the property key is of string type. function changePersonData< Obj extends Person, Key extends Extract<keyof Perso...