ts复制代码// 判断是否是函数functionis_callable<TextendsFunction>(target:any):targetisT{returntypeoftarget==='function'}functionmatch_range<T>(n:number,pattern:Record<string,T|((start:number,end:number)=>T)>){for(constpinpattern){constrange=newRange(p)if(range.is_between(n)){consthandle...
复制 functionvalidateField(target:any,propertyName:string){constoriginalValue=target[propertyName];Object.defineProperty(target,propertyName,{get(){returnoriginalValue;},set(value:any){// 进行字段验证if(isValid(value)){originalValue=value;}else{thrownewError(`Invalid value for${propertyName}`);}},}...
functionadd(a:number,b:number):number;functionadd(a:string,b:string):string;functionadd(a:string,b:number):string;functionadd(a:number,b:string):string;functionadd(a:Combinable,b:Combinable){// type Combinable = string | number;if(typeofa==='string'||typeofb==='string'){returna.toStri...
functionsanitizeFoo(checker:any){if(typeofchecker.number=="string"&&Boolean(checker.number.trim())&&!Number.isNaN(Number(checker.number))){checker.number=Number(checker.number);}if(typeofchecker.boolean=="string"&&(checker.boolean=="true"||checker.boolean=="false")){checker.boolean=checker.boo...
TypeScript can usually figure out a more specific type for a variable based on checks that you might perform. This process is called narrowing. Copy functionuppercaseStrings(x:string| number) {if(typeofx==="string") {// TypeScript knows 'x' is a 'string' here.returnx.toUpperCase(); ...
function printId(id: number | string): void { console.log(`ID: ${id}`); } printId(123); // Output: "ID: 123" printId('abc'); // Output: "ID: abc" 延伸阅读:TypeScript 官方手册——联合类型(https://www.typescriptlang.org/docs/handbook/unions-and-intersections.html) ...
| numberis assignable tostring(which isn’t the case –stringis a subtype ofstring | number). Excluding methods from the check allows TypeScript to continue modeling the above use-cases (e.g. event handlers and simpler array handling) while still bringing this much-demanded strictness check. ...
functionisString(s){returntypeofs==='string';} step 2 Use the isString function inside another function: 在另外一个函数中使用上面的函数(isString()) 代码语言:javascript 复制 functiontoUpperCase(x:unknown){if(isString(x)){x.toUpperCase();// ⚡️ x is still of type unknown}} ...
The following example performs the necessary check to determine thatrandomValueis astringbefore using type assertion to call thetoUpperCasemethod. TypeScriptCopy letrandomValue: unknown =10; randomValue =true; randomValue ='Mateo';if(typeofrandomValue ==="string") {console.log((randomValueasstring...
functionf(x:string|number|boolean){constisString=typeofx==="string";constisNumber=typeofx==="number";constisStringOrNumber=isString||isNumber;if(isStringOrNumber){x;// Type of 'x' is 'string | number'.}else{x;// Type of 'x' is 'boolean'.}} ...