functionprintValue(value:string|number):void{if(typeofvalue ==='string') {console.log(`The value is a string:${value}`);}elseif(typeofvalue ==='number') {console.log(`The value is a number:${value}`);}}classPerson {name:string;...
1.typeof类型守卫 typeof是一种简单且常用的类型守卫,适用于基本类型(如string、number、boolean等)。通过typeof,我们可以判断变量的具体类型并进行处理。 示例代码 functionprocessValue(value:string|number):void{if(typeofvalue==="string"){console.log(value.toUpperCase());// 确定是字符串类型}else{console....
interface是JavaScript中的“未来保留关键字”。Javascript不允许将其用作标识符，以便可以将其用作关键字...
const isString = (val: unknown): val is string => typeof val === 'string'; const isSymbol = (val: unknown): val is symbol => typeof val === 'symbol'; const isFunction = (val: unknown): val is Function => typeof val === 'function'; const isObject = (val: unknown): va...
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...
*/functiontoObject(key,value){return{[key]:value};} 类型守卫: 代码语言:javascript 代码运行次数:0 运行 AI代码解释 /** * @param {any} value * @return {value is YOUR_TYPE} */functionisYourType(value){letisType;/** * Do some kind of logical testing here ...
则访问任何属性都会产生编译时错误: function getLength(s: string | null) { // Error: Object 可能为空 return s.length; } 在访问属性之前,需要使用类型保护来检查给定对象上的属性访问是否安全: function getLength(s: string | null) { if (s === null) { return 0; } return s.length; } Type...
In JavaScript, it is a runtime error to use a non-object type on the right side of the in operator. TypeScript 4.2 ensures this can be caught at design-time. Copy "foo" in 42 // ~~ // error! The right-hand side of an 'in' expression must not be a primitive. This check is...
// 源码 function getMetadata(metadataKey, target, propertyKey) { if (!IsObject(target)) throw new TypeError(); if (!IsUndefined(propertyKey)) propertyKey = ToPropertyKey(propertyKey); return OrdinaryGetMetadata(metadataKey, target, propertyKey); } function getOwnMetadata(metadataKey, target, ...
interface Checkable { check(name: string): boolean; } class NameChecker implements Checkable { check(s) { // Parameter 's' implicitly has an 'any' type. // Notice no error here return s.toLowercse() === "ok"; // any } }