「TypeScript」的原始类型包括:「boolean、number、string、void、undefined、null、symbol、bigint。」 需要注意的是,number是类型,而Number是构造函数。 当函数没有返回值时,返回类型就是void。只有null和undefined可以赋给void。 默认情况下null和undefined是所有类型的子类型。开启--strictNullChecks后,null和undefined...
function isEmpty(value) { // 对于null也认为是空对象,返回true if (value == null) { return true; } // 对数组/类数组对象/字符串/Buffer/arguments对象,根据length属性进行判断 if (isArrayLike(value) && (isArray(value) || typeof value == 'string' || typeof value.splice == 'function' ...
Type-checking can catch all sorts of issues like typos and forgetting to check for null and undefined. But types go beyond type-checking – the same analyses of TypeScript’s type-checker are used for rich editor tooling like auto-completion, code navigation, and refactorings. In fact, if ...
function isString(x: any): x is string { return typeof x === "string"; } 五、联合类型和类型别名 5.1 联合类型 联合类型通常与null或undefined一起使用: const sayHello = (name: string | undefined) => { /* ... */ }; 例如,这里name的类型是string | undefined意味着可以将string或undefined...
let obj: unknown = null; obj.getCoordinate(); // 报错:obj类型为 unknown (obj as { getCoordinate: () => string }).foo(); // ok never:代表无类型,不带类型信息,常见的是 throwerror 函数。 function throwError(): never { throw new Error() } 有时候也可以用它来做流程分支运行时安全/错...
functionf(x:string|number|boolean){constisString=typeofx==="string";constisNumber=typeofx==="number";constisStringOrNumber=isString||isNumber;if(isStringOrNumber){x;// 'x'的类型为'string | number'。}else{x;// 'x'的类型为'boolean'。}} ...
functiongreet(name:string, message:string= 'Hello', times?:number):void{for(leti =0; i < (times ||1); i++) {console.log(`${message},${name}!`);}}greet('John');// Output: "Hello, John!"greet('Jane','Hi');// Output: ...
asyncFactory: Function | void; // async component factory functionasyncMeta: Object | void;isAsyncPlaceholder: boolean;ssrContext: Object | void;fnContext: Component | void; // real context vm for functional nodesfnOptions: ?ComponentOptions; // for SSR cachingfnScopeId: ?string; // ...
final String beanName = transformedBeanName(name); Object bean; // Eagerly check singleton cache for manually registered singletons. //从缓存中获取bean实例 Object sharedInstance = getSingleton(beanName); if (sharedInstance != null && args == null) { ...