functiontoUpperCase(x:unknown){if(isString(x)){x.toUpperCase();// ⚡️ x is still of type unknown}} TypeScript throws an error. We can be sure that x is of type string at this point. But since the validation
interfaceUser{name:string age?:number// 可选属性readonly isMale:boolean// 只读属性} 函数类型 代码语言:javascript 代码运行次数:0 运行 AI代码解释 interfaceSay{(words:string):string}interfaceUser{name:string age?:number readonly isMale:booleansay:(words:string)=>stringsay:Say// 或者使用接口描述函...
constarr:string[] = ['a','b','c'];console.log(Array.isArray(arr));// 👉️ true Array.isArray方法返回一个布尔结果 - 如果传入的值是一个数组,则返回true,否则返回false。 NaN(不是数字)的类型是数字。 如果我们需要检查特定值是否为NaN,请使用Number.isNaN方法。 constexample =Number('hello...
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:${permission}`);}returnneworiginalConstructor(...args);};newC...
if (typeof foo === "string") { // 这里 foo 被收窄为 string 类型 } else if (typeof foo === "number") { // 这里 foo 被收窄为 number 类型 } else { // foo 在这里是 never const check: never = foo; } } 注意在 else 分支里面,我们把收窄为 never 的 foo 赋值给一个显示声明的...
number = null; function check(x, name) { if (x == null) { console.log(name + ' == null'); } if (x === null) { console.log(name + ' === null'); } if (typeof x === 'undefined') { console.log(name + ' is undefined'); } } check(a, 'a'); check(b, 'b');...
functionprintValue(value:string|number):void{if(typeofvalue ==='string') {console.log(`The value is a string:${value}`);}elseif(typeofvalue ==='number') {console.log(`The value is a number:${value}`);}}classPerson {name:string;...
function sanitizeFoo(checker: any) { if ( typeof checker.number == "string" && Boolean(checker.number.trim()) && !Number.isNaN(Number(checker.number)) ) { checker.number = Number(checker.number); } if ( typeof checker.boolean == "string" && (checker.boolean == "true" || checker...
Use the find() Method to Check if a String Is Present in a TypeScript ArrayThe find() method returns the first occurrence of the target element if it successfully executes, or else it returns undefined.var fruitsArray : string[] = ['apple', 'orange', 'lichi', 'banana']; if(fruitsAr...
toString():string; toLocaleString():string; valueOf(): Object; hasOwnProperty(v: PropertyKey): boolean; isPrototypeOf(v: Object): boolean; propertyIsEnumerable(v: PropertyKey): boolean; } 2.2:ObjectConstructor 接口定义了 Object 类的属性