为什么我在Typescript定义的类上的属性显示为未定义？

Question

我有一个我在组件类中定义的属性options ，但是当我在浏览器中运行代码时，它显示为未定义。 我在代码上找不到任何逻辑上错误的地方，但是认为这可能是某种错误或版本控制问题。

这是组件类：

 import { Component, OnInit, Input } from '@angular/core'; import { FormControl } from '@angular/forms'; import { Observable } from 'rxjs/Observable'; import 'rxjs/add/operator/startWith'; import 'rxjs/add/operator/map'; @Component({ selector: 'app-selector', templateUrl: './selector.component.html', styleUrls: ['./selector.component.css'] }) export class SelectorComponent implements OnInit { myControl = new FormControl(); selectedOption: any; filteredOptions: Observable<any[]>; @Input() optionTitle: string; options: [ { name: 'something' }, { name: 'something else' } ]; constructor() { } ngOnInit() { this.filteredOptions = this.myControl.valueChanges .startWith(null) .map(item => item && typeof item === 'object' ? item.name : item) // this is where it's saying this.options is undefined. // (if I do console.log(this.optionTitle), that shows up perfectly fine) .map(name => name ? this.filter(name) : this.options.slice()); } filter(input: string): any[] { return this.options.filter(option => option.name.toLowerCase().indexOf(input.toLowerCase()) === 0); } displayFn(option: any): string | any { return option ? option.name : option; } select($event): void { this.selectedOption = $event.option.value; } } 

这是我在浏览器中遇到的错误：

 SelectorComponent.html:3 ERROR TypeError: Cannot read property 'slice' of undefined at MapSubscriber.project (selector.component.ts:35) at MapSubscriber.webpackJsonp.../../../../rxjs/operator/map.js.MapSubscriber._next (map.js:77) at MapSubscriber.webpackJsonp.../../../../rxjs/Subscriber.js.Subscriber.next (Subscriber.js:89) at MapSubscriber.webpackJsonp.../../../../rxjs/operator/map.js.MapSubscriber._next (map.js:83) at MapSubscriber.webpackJsonp.../../../../rxjs/Subscriber.js.Subscriber.next (Subscriber.js:89) at MergeAllSubscriber.webpackJsonp.../../../../rxjs/OuterSubscriber.js.OuterSubscriber.notifyNext (OuterSubscriber.js:19) at InnerSubscriber.webpackJsonp.../../../../rxjs/InnerSubscriber.js.InnerSubscriber._next (InnerSubscriber.js:23) at InnerSubscriber.webpackJsonp.../../../../rxjs/Subscriber.js.Subscriber.next (Subscriber.js:89) at Object.subscribeToResult (subscribeToResult.js:17) at MergeAllSubscriber.webpackJsonp.../../../../rxjs/operator/mergeAll.js.MergeAllSubscriber._next (mergeAll.js:85) 

这里可能出什么问题了？

Answer 1

通过查看您的代码，我怀疑您需要替换

options:

同

options =

Answer 2

您永远不会初始化任何option ，您已经有了：

options: [
  {
    name: 'something'
  },
  {
    name: 'something else'
  }
];

但是我想你想要的是

options = [
  {
    name: 'something'
  },
  {
    name: 'something else'
  }
];

第二个初始化该字段，而第一个只是一个类型定义（（大致等同于options: Array<{name: 'something' | 'something else'}> ））