javascript - typescript /Angular : Filter array of objects

Question

我有一个对象数组。我的对象有一个“类别”属性。我想过滤对象数组以仅返回具有“技术”类别的对象。

抛出的错误是类型 {} 上不存在“filter”

stocks-list.ts

import { Stock } from './Stock';

export const STOCKS: any[] = [
  { id: 11, symbol: 'AAPL', name: 'Apple', category: 'Tech' },
];

stock.service.ts

import { Injectable } from '@angular/core';
import { Stock } from './Stock';

import { STOCKS } from './stocks-list';

@Injectable({
  providedIn: 'root'
})


export class StockService {


  constructor() { }
  techStocks: Stock[];
  getTechStocks(): Stock[] {
    this.techStocks = STOCKS;


    return this.techStocks.filter(xx => xx.category = 'Tech');
  }
}

Answer 1

您只需将 xx.category = 'Tech' (谁更新)替换为 xx.category === 'Tech' (谁测试平等)

简单的可重现示例:

const stocks = [
  { id: 11, symbol: 'AAPL', name: 'Apple', category: 'Tech' },
  { id: 12, symbol: 'AAPL', name: 'Orange', category: 'Fruit' },
  { id: 13, symbol: 'AAPL', name: 'Not Apple', category: 'Fruit' },
];
console.log(stocks.filter(xx => xx.category = 'Tech'));

在这种情况下，您将每个元素的类别更新为“Tech”(查看第一个片段的结果，所有类别现在都是“Tech”)，然后将“Tech”返回到始终为“true”的过滤器函数

    console.log(foo = "bar"); // Assignment also return the value
    console.log(!!foo); // A non-null value is `true` (as boolean)

因此，您的过滤函数将始终测试 if (!!'Tech' === true) (始终 true)，因此返回每个更新的元素。

您只需要使用===即可返回正确的 bool 值

const stocks = [
  { id: 11, symbol: 'AAPL', name: 'Apple', category: 'Tech' },
  { id: 12, symbol: 'AAPL', name: 'Orange', category: 'Fruit' },
  { id: 13, symbol: 'AAPL', name: 'Not Apple', category: 'Fruit' },
];
console.log(stocks.filter(xx => xx.category === 'Tech'));