ts 抛出了一个错误提示,我们能确信 x 是在类型判断为 string 以后再进行 toupperCase().但是由于这个检验函数(isString)被包裹在 toUpperCase()函数中,ts 在判断的时候还是抛出了错误提示。。 Let’s tell TypeScript explicitly that if isString evaluates to true, the type of the parameter is a string: ...
AI代码解释 functioncheckPermission(permission:string){returnfunction(target:any){constoriginalConstructor=target;constnewConstructor=function(...args:any[]){// 检查用户权限的逻辑if(!hasPermission(permission)){thrownewError(`没有权限进行操作:${permission}`);}returnneworiginalConstructor(...args);};newC...
Number.isNaN(Number(checker.number)) ) { checker.number = Number(checker.number); } if ( typeof checker.boolean == "string" && (checker.boolean == "true" || checker.boolean == "false") ) { checker.boolean = checker.boolean == "true"; } if ( typeof checker.number != "number"...
function printValue(value: string | number): void { if (typeof value === 'string') { console.log(`The value is a string: ${value}`); } else if (typeof value === 'number') { console.log(`The value is a number: ${value}`); } } class Person { name: string; constructor(na...
if (typeof foo === "string") { // 这里 foo 被收窄为 string 类型 } else if (typeof foo === "number") { // 这里 foo 被收窄为 number 类型 } else { // foo 在这里是 never const check: never = foo; } } 注意在 else 分支里面,我们把收窄为 never 的 foo 赋值给一个显示声明的...
{suit: string; card: number; }[]): number; function pickCard(x: number): {suit: string; card: number; }; function pickCard(x): any { // Check to see if we're working with an object/array // if so, they gave us the deck and we'll pick the card if (typeof x == "...
interface A { a: string; } interface B { b: string; } type MyType = A | B; function isA(x: MyType): x is A { return "a" in x; } function someFn(x: MyType) { if (isA(x) === true) { console.log(x.a); // works! } } We’d like to thank Mateusz Burzyński fo...
This means that if you expect the type to be string | number but the argument is of type string, the tests will fail. import {expectType} from 'tsd'; import concat from '.'; expectType<string>(concat('foo', 'bar')); expectType<string | number>(concat('foo', 'bar')); If we...
class SafeBox { #value: string | undefined; // Only accepts strings! set value(newValue: string) { } // Must check for 'undefined'! get value(): string | undefined { return this.#value; } } In fact, this is similar to how optional properties are checked under --exactOptionalPrope...
As you can see we have a number, boolean and a string. But what happens if we try to set them in the wrong order:Example // define our tuple let ourTuple: [number, boolean, string]; // initialized incorrectly which throws an error ourTuple = [false, 'Coding God was mistaken', 5...