typescript中syntax []的含義是什么

Question

我想使用離子樣本應用程序來構建一個Web應用程序。 有一部分示例代碼用typescript編寫。 我無法理解這個[f] = fields [f]代碼的含義你能解釋一下這段代碼的含義嗎？

這個ts文件的完整代碼是：

  /**
 * A generic model that our Master-Detail pages list, create, and delete.
 *
 * Change "Item" to the noun your app will use. For example, a "Contact," or 
 a
 * "Customer," or a "Animal," or something like that.
 *
 * The Items service manages creating instances of Item, so go ahead and 
rename
 * that something that fits your app as well.
 */
export class Item {

  constructor(fields: any) {
    // Quick and dirty extend/assign fields to this model
    for (const f in fields) {
      // @ts-ignore
      this[f] = fields[f];
    }
  }

 }

export interface Item {
  [prop: string]: any;
}

Answer 1

您正在查看動態屬性訪問器。 說“fields”是{first: 1, second: 2} ，代碼相當於：

this.first = fields.first this.second = fields.second

簡而言之，它將字段的所有可枚舉屬性分配給此。

MDN Web文檔：屬性訪問者

Answer 2

將其視為通用構造函數。 它的作用是迭代函數范圍中別名“fields”的對象成員，並將值分配給“this”，這是創建的對象。 例如，如果傳遞的對象是：

var fields= {mem1: 1, mem2: 'marios'};

the code would then

for (const f in fields) {
      this[f] = fields[f];
      // 1st iteration would be
      // this[mem1] =  fields[mem1]; -> this[mem1] will create the property to the new object
      // fields[mem1] will read the value, so it created the prop and copies the value 
    }

Answer 3

這是屬性訪問的括號表示法。 您可以在此處了解有關MDN的更多信息