When working with conditionals types, within the “extends” expression, we can use the “infer” keyword to either get the type of the elements of an array, or even to get the return type of a function. We can use this to build a “FnReturnType” type, that will give us the return...
判断js中的数据类型有一下几种方法:typeof、instanceof、 constructor、Object.prototype.toString。这篇文章来分析一下这几种方式底层原理,比较一下他们的区别。 二、typeof typeof 是最常用的判断数据类型的方法,我们可以利用 typeof 来判断number, string, object, boolean, function, undefined, symbol 这七种类型。
1.typeof() 适用于判断除了null外的基础类型和function 可以判断数据类型,它返回表示数据类型的字符串(返回结果只能包括number,boolean,string,function,object,undefined) 可以使用typeof判断变量是否存在(如if(typeof a!=“undefined”){…}) 无法判断对象和数组,两者都返回object typeof '5' // string typeof 5...
ReturnType<Type> 获取函数类型的返回值类型。 实现为: 代码语言:javascript 代码运行次数:0 运行 AI代码解释 /** * Obtain the return type of a function type */type ReturnType<Textends(...args:any)=>any>=Textends(...args:any)=>inferR?R:any; 等号左侧的(...args: any) => any代表一个任...
function add(x: number, y: number): number { return x + y; } let myAdd = function (x: number, y: number): number { return x + y; }; 2.1.2. Writing the function type A function’s type has the same two parts: the type of the arguments and the return type. When writing ou...
function reverse(x: string): string function reverse(x: number): number function reverse(target: string | number) { if (typeof target === 'string') { return target.split('').reverse().join('') } if (typeof target === 'number') { return +[...target.toString()].reverse().join...
function f() { return { x: 10, y: 3 }; } type P = ReturnType<f>; // 'f' refers to a value, but is being used as a type here. 这是因为值(values)和类型(types)并不是一种东西。为了获取值 f 也就是函数 f 的类型,我们就需要使用 typeof: ...
typeOneArgFn<A=any>=(firstArg:A,..._args:any[])=>voidtypeGetFirstArg<T>=TextendsOneArgFn<inferR>?R:never;// Test casefunctionfoo(x:string,y:number){returnnull}// ^?typet1=GetFirstArg<typeoffoo>// ^? string 分类:TypeScript ...
functionarea(shape:string,width:number,height:number){vararea=width*height;return"I'm a "+shape+" with an area of "+area+" cm squared.";}document.body.innerHTML=area("rectangle",30,15); 接下来,修改index.html的 js 文件为type.js然后编译 TypeScript 文件:tsc type.ts。
The type of the value returned by the function can be explicitly defined.ExampleGet your own TypeScript Server // the `: number` here specifies that this function returns a number function getTime(): number { return new Date().getTime(); } Try it Yourself » ...