类型化数组的使用

我有一个 TypeScript 类定义，它是这样开始的;

module Entities {


export class Person {
private _name: string;
private _possessions: Thing[];
private _mostPrecious: Thing;


constructor (name: string) {
this._name = name;
this._possessions = new Thing[100];
}

看起来一个 Thing 类型的数组没有被正确地转换成相应的 Javascript 数组类型。下面是生成的 JavaScript 的一个片段:

function Person(name) {
this._name = name;
this._possessions = new Entities.Thing[100]();
}

执行包含 Person 对象的代码时，在尝试初始化 _ holdings 字段时引发异常:

错误是“0x800a138f-Microsoft JScript 运行时错误: 无法获取属性‘100’的值: 对象为 null 或未定义”。

如果我将 _ holdings 的类型更改为 any[]，并且使用 new Array()异常初始化 _ holdings，则不会引发异常。我错过什么了吗？

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小开

The translation is correct, the typing of the expression isn't. TypeScript is incorrectly typing the expression new Thing[100] as an array. It should be an error to index Thing, a constructor function, using the index operator. In C# this would allocate an array of 100 elements. In JavaScript this calls the value at index 100 of Thing as if was a constructor. Since that values is undefined it raises the error you mentioned. In JavaScript and TypeScript you want new Array(100) instead.

You should report this as a bug on CodePlex.

小开
最佳答案

You have an error in your syntax here:

this._possessions = new Thing[100]();

This doesn't create an "array of things". To create an array of things, you can simply use the array literal expression:

this._possessions = [];

Of the array constructor if you want to set the length:

this._possessions = new Array(100);

I have created a brief working example you can try in the playground.

module Entities {


class Thing {


}


export class Person {
private _name: string;
private _possessions: Thing[];
private _mostPrecious: Thing;


constructor (name: string) {
this._name = name;
this._possessions = [];
this._possessions.push(new Thing())
this._possessions[100] = new Thing();
}
}
}
小开

There are two syntax options available when declaring an array in typescript. The typescript docs uses Array<T> however ts-lint prefers T[]

By using the Array<Thing> it is making use of the generics in typescript. It is similar to asking for a List<T> in c# code.

// Declare with default value
private _possessions: Array<Thing> = new Array<Thing>(); // or
private _possessions: Array<Thing> = []; // or
private _possessions: Thing[] = []; // or -> prefered by ts-lint

or

// declare then assign in the constructor
private _possessions: Array<Thing>; // or
private _possessions: Thing[]; // or -> preferd by ts-lint
  

constructor(){
this._possessions = new Array<Thing>(); // or
this._possessions = []; // or
}

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