是否可以为打字稿中的接口函数提供默认参数？

Question

我将数字 class 扩展如下：

interface Number {
    evolution(now: number, before: number): string;
}


Number.prototype.magnitude = function(d=1, suffix="") {
    //…
}

而且我喜欢提供默认参数。

但是在没有显式参数的情况下使用它时如下：

label = "÷ " + show.magnitude();

我收到一个错误"The supplied parameters do not match signature"

Answer 1

你需要告诉TypeScript编译器参数是optional:

In JavaScript, every parameter is optional, and users may leave them off as they see fit. When they do, their value is undefined. We can get this functionality in TypeScript by adding a ? to the end of parameters we want to be optional.

下面是一个类似于您要完成的示例：

interface ISum {
    (baz?: number, buz?: number): number;
}

let sum: ISum = (baz = 1, buz = 2) => {
    return baz + buz;
}

console.log(sum()); //Console: 3
console.log(sum(2)); //Console: 4
console.log(sum(2, 7)); //Console: 9

是否可以为打字稿中的接口函数提供默认参数？

Is it possible to provide default parameter to interface function in typescript?

typescript

interface

default-parameters