typescript 打字稿：通过传入命名参数的构造函数创建类？
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Typescript: Create class via constructor passing in named parameters?
提问by Martin
I have a class where I have the constructor defined with 3 parameters which are all optional. I was hoping to be able to pass in named parameters so I don't need to pass in undefined.
我有一个类，其中的构造函数定义了 3 个参数，这些参数都是可选的。我希望能够传入命名参数，所以我不需要传入 undefined。
constructor(year?: number,
month?: number,
date?: number)
I was hoping to create an intance of the class like so
我希望像这样创建一个类的实例
const recurrenceRule = new MyNewClass(month: 6)
but it didn't work and i tried
但它没有用，我试过了
const recurrenceRule = new MyNewClass(month = 6)
and that didn't work.
那没有用。
The only way i got it to work was either
我让它工作的唯一方法是
const recurrenceRule = new MyNewClass(undefined, 4)
or
或者
const recurrenceRule = new MyNewClass(, 4)
But it seems so messy, I was hoping to pass in named arguments and becasue they are all optional I should be able to just pass in 1 - right ?
但它看起来很乱，我希望传入命名参数，因为它们都是可选的，我应该能够传入 1 - 对吗？
回答by SVSchmidt
You can use Object destructuring introduced in ES6 to archieve the desired behavior: reference. TypeScript is able to transpile this feature for usage with ES5 to target older browsers. However, as of ES6, this is also perfectly valid JavaScript.
您可以使用 ES6 中引入的对象解构来归档所需的行为：引用。TypeScript 能够将此功能转译为与 ES5 一起使用，以针对较旧的浏览器。然而，从 ES6 开始，这也是完全有效的 JavaScript。
Basically, it looks like this: constructor({ year, month, day})and is invoked, for instance, as new Bar({ year: 2017 }). Then you can access yearas a variable within the constructor, e.g. for assigning this.year = year.
基本上，它看起来像这样：constructor({ year, month, day})并且被调用，例如，作为new Bar({ year: 2017 })。然后您可以year在构造函数中作为变量访问，例如分配this.year = year.
More interesting than that is the usage with default values, e.g.
比这更有趣的是使用默认值，例如
constructor({ year = new Date().getFullYear(),
month = new Date().getMonth(),
day = new Date().getDay()
} = {})
which allows invoking the constructor with 0, 1, 2 or 3 parameters respectively (see snippet below).
它允许分别使用 0、1、2 或 3 个参数调用构造函数（参见下面的代码片段）。
The somewhat cryptic = {}is for the case when you create a new instance without any parameters. First, {}is used as the default value for the parameter object. Then, since yearis missing, the default value for that one is added, then for month and for day respectively.
有点神秘的= {}是当您创建一个没有任何参数的新实例时。首先，{}用作参数对象的默认值。然后，由于year缺少，添加了那个的默认值，然后分别为月和日。
For usage with TypeScript, you can, of course, add additional typings,
为了与 TypeScript 一起使用，您当然可以添加其他类型，
constructor({ year = new Date().getFullYear(),
month = new Date().getMonth(),
day = new Date().getDay()
}: { year?: number, month?: number, day?: number } = {}) {
...
}
Although this reallylooks cryptic.
虽然这看起来真的很神秘。
class Bar {
constructor({ year, month, day }) {
this.year = year;
this.month = month;
this.day = day;
}
log () {
console.log(`year: ${this.year}, month: ${this.month}, day: ${this.day}`);
}
}
new Bar({ day: 2017 }).log();
class Foo {
constructor({ year = new Date().getFullYear(),
month = new Date().getMonth(),
day = new Date().getDay()
} = {}) {
this.year = year;
this.month = month;
this.day = day;
}
log () {
console.log(`year: ${this.year}, month: ${this.month}, day: ${this.day}`);
}
}
console.log('with default value:');
new Foo().log();
new Foo({ day: 2 }).log();
new Foo({ day: 2, month: 8 }).log();
new Foo({ year: 2015 }).log();回答by elm
class Bar {
constructor({a, b}: {a?: number, b?: number}) {}
}
new Bar({b: 1})
For more information, see ES6 Object Destructuring with functions.
有关更多信息，请参阅ES6 Object Destructuring with functions。
回答by Paul Grimshaw
Simple parameter:
简单参数：
constructor (private recurrenceSettings: {year?: number, month?: number, date?: number})
The private keyword instantiates argument as an instance variable, saving you needing to instantiate in the constructor. Can also be publicif you want to instatiate public properties.
private 关键字将参数实例化为实例变量，省去了在构造函数中实例化的需要。public如果您想实例化公共属性，也可以是。
Use like this:
像这样使用：
const recurrenceRule = new MyClass({month: 12})
Or use destructuring (usage same as above):
或者使用解构（用法同上）：
constructor({day, month, year}: {day?: number, month?: number, year?: number})
The above version loses the ability to use the private/public shortcut for instance variables though (see https://github.com/Microsoft/TypeScript/issues/5326).
尽管上面的版本失去了对实例变量使用私有/公共快捷方式的能力（请参阅https://github.com/Microsoft/TypeScript/issues/5326）。
