Enums in TypeScript 2+ lost value when send from html

Question

I have an object and enum defined like this:

export interface Character {
  name: string;
  side: Side;
}

export enum Side {
  All,
  Light,
  Dark
}

I am using this enum in my component:

import { Component, OnInit } from '@angular/core';
import { Character, Side } from '../core';

@Component({
  selector: 'app-tabs',
  templateUrl: './tabs.component.html'
})
export class TabsComponent {
  chosenList = Side.All; // initial value set to 0

  characters = [
    { name: 'Luke Skywalker', side: Side.All }, // side is set to 0
    { name: 'Darth Vader', side: Side.All } // side is set to 0
  ];

  onChoose(side: Side): void {
    this.chosenList = side; // this line goes wrong set chosenList to string 'Side.All'
  }

  getCharacters(): Character[] {
    if (this.chosenList === Side.All) {
      return this.characters.slice();
    }
    return this.characters.filter((character) => {
      return character.side === this.chosenList;
    });
  }

  onSideChosen(charInfo: Character): void {
    const pos = this.characters.findIndex((char) => {
      return char.name === charInfo.name;
    });
    this.characters[pos].side = charInfo.side;
  }
}

My html looks like this. The problem lies in (click) event. I pass enum like this to my component unfortunately my component resolve it as string.

<div id="tab-main" class="container">
  <ul class="nav nav-tabs">
    <li class="nav-item">
      <a [ngClass]="{active: chosenList === 'Side.All'}" class="nav-link" (click)="onChoose('Side.All')" style="cursor: pointer">All</a>
    </li>
    <li class="nav-item">
      <a [ngClass]="{active: chosenList === 'Side.Light'}" class="nav-link" (click)="onChoose('Side.Light')" style="cursor: pointer">Light</a>
    </li>
    <li class="nav-item">
      <a [ngClass]="{active: chosenList === 'Side.Dark'}" class="nav-link" (click)="onChoose('Side.Dark')" style="cursor: pointer">Dark</a>
    </li>
  </ul>
  <app-list [characters]="getCharacters()" (sideAssigned)="onSideChosen($event)"></app-list>
</div>

The problem is when I click on button "All button" this line of code is invoked

onChoose(side: Side): void {
    this.chosenList = side; // this line goes wrong set chosenList to string 'Side.All'
  }

however when I compare values like this

if (this.chosenList === Side.All)

it always return false because chosenList is not enum anymore but it's string.

My question is how can I pass enum from .html file to .ts I know I can resolve this problem just by sending 0 / 1 / 2 within html however this way I am loosing readability...

Answer 1

1. declare field variable public Side = Side; in the component
2. import Side from the file where it's defined
3. change template reference to "{active: chosenList === Side.All}"

The problem is basically that in templates you don't have access to stuff defined outside the component especially if it has to be transpiled first