if (typeof strOrNumOrBool === "string") { console.log("str!"); } else if (typeof strOrNumOrBool === "number") { console.log("num!"); } else if (typeof strOrNumOrBool === "boolean") { console.log("bool!"); } else { const _exhaustiveCheck: never = strOrNumOrBool;...
very dangerous}functionformat2(value:unknown){value.toFixed(2);// 代码会飘红,阻止你这么做// 你需要收窄类型范围,例如:// 1、类型断言 —— 不飘红,但执行时可能错误(valueasNumber).toFixed(2);// 2、类型守卫 —— 不飘红,且确保正常执行if(typeofvalue==='number'){// 推断出类型: numbervalue...
never。never类型表示的是那些永不存在的值的类型,never类型是任何类型的子类型,也可以赋值给任何类型;然而,没有类型是never的子类型或可以赋值给never类型(除了never本身之外)。示例如下: 代码语言:javascript 代码运行次数:0 运行 AI代码解释 // 抛出异常的函数永远不会有返回值functionerror(message:string):never{...
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;...
functionprocessValue(value:string|number):void{if(typeofvalue==="string"){console.log(value.toUpperCase());// 确定是字符串类型}else{console.log(value.toFixed(2));// 确定是数字类型}} 1. 2. 3. 4. 5. 6. 7. 在这个例子中,typeof帮助我们区分了string和number类型,从而避免了类型错误。
When checking if a union is assignable to some target type, we have to check if every member of the union is assignable to the target type, and that can be very slow. In TypeScript 5.3, we peek at the original intersection form that we were able to tuck away. When we compare the ...
type IsNameKey = CheckKey<Person, 'name'>; // Result: true type IsCityKey = CheckKey<Person, 'city'>; // Result: false 在此示例中,CheckKey 是一个条件类型,用于检查提供的键是否为“name”。 延伸阅读:TypeScript 官方手册 — keyof Type Operator、TypeScript 官方手册 — in Operator(https:...
If you're not familiar with TypeScript, it's a language that builds on top of JavaScript by adding syntax for types. Writing types in our code allows us to explain intent and have other tools check our code to catch mistakes like typos, issues with and , and more. Types also power.....
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,never只能赋值给never const check: never = foo; ...
问题原因 当我们声明一个空数组而不显示键入它并尝试向其中添加元素时,会发生该错误。 解决方案 声明数组类型即可 参考链接 https://bobbyhadz.com/blog/typescript-argument-type-not-assignable-parameter-type-never