functionf(x:string|number|boolean){constisString=typeofx==="string";constisNumber=typeofx==="number";constisStringOrNumber=isString||isNumber;if(isStringOrNumber){x;// 'x'的类型为'string | number'。}else{x;// 'x'的类型为'boolean'。}} 请注意,新机制的深度是有极限的——TypeScript 在...
b:number):string;functionadd(a:number,b:string):string;functionadd(a:Combinable,b:Combinable){// type Combinable = string | number;if(typeofa==='string'||typeofb==='string'){returna.toString()+b.toString();}returna+b;}
classApple{/** 数量 */count=0;/** 单价 */price=2.0;staticgetPrice(apple:Apple,bagPrice:number){returnapple.count*apple.price+bagPrice;}}classShopping{apple=newApple;peopleNum=3;staticgetPrice(shopping:Shopping){returnApple.getPrice(shopping.apple+0.1)/shopping.peopleNum;}} 思想篇 TypeScript ...
function padLeft(value: string, padding: string | number) { if (typeof padding === "number") { return Array(padding + 1).join(" ") + value; } if (typeof padding === "string") { return padding + value; } throw new Error(`Expected string or number, got '${padding}'.`); }...
functionsanitizeFoo(checker:any){if(typeofchecker.number!="number"||typeofchecker.boolean!="boolean"||(checker.maybeString!=undefined&&typeofchecker.maybeString!="string")||!sanitizeBar(checker.bar)){returnfalse;}returntrue;}functionsanitizeBar(checker:any){if(!sanitizenumberArray(checker.numbers)...
export type BasicPrimitive = number | string | boolean; export function doStuff(value: BasicPrimitive) { let x = value; return x; } If we hover our mouse over x in an editor like Visual Studio, Visual Studio Code, or the TypeScript Playground, we’ll get a quick info panel that shows...
I came across a problem of converting a char value to a number when I was working with Javascript. The interesting thing was that the solution just wasn’t as obvious as I initially thought. In this post, I will talk about how I solved the problem to check a string is numeric in ...
// Returns '{ name: string, age: number, greeting: string } & T' function foo<T>(obj: T) { let person = { name: "Daniel", age: 26 }; return { ...person, greeting: "hello", ...obj }; } Object rest on generic types ...
Comparing number- and string-based enums A subtle difference between number-based enums and string-based enums is that number-based enums have reverse mapping for number-valued members. Reverse mapping allows us to check if a given value is valid in the context of the enum. To better under...
interface ICustomerShort { Id: number; CalculateDiscount( discountAmount: ( discountClass: string, multipleDiscount: boolean ) => number): number } That parameter is defined using a function type that accepts two parameters (one of string, one of boolean) and returns a number. If you’re a...