How to create a static constant in a class using TypeScript?

Question

How to create an TypeScript static constant in a class? That mean I can refer a constant without initialize the class. This is my class:

export class CallTree{
    public static readonly active = 1;
    ............................
}

The component's html is something like the following:

 <table mat-table [dataSource]="callTreeList" matSort class="mat-elevation-z8 callTreeList">
    ...............................

  <ng-container matColumnDef="status">
    <th mat-header-cell *matHeaderCellDef mat-sort-header>Status</th>
    <td mat-cell *matCellDef="let element" [innerHTML]="(element.status === CallTree.active)?'Active':'Inactive'"></td>
   </ng-container>

The browser console prompt the following error message:

TypeError: Cannot read property 'active' of undefined

How can I fix the problem? How can I use this constant in the Angular component's html?

I don't think your declaration of static const is wrong, as @LloydNicholson said, from where you are calling it might be wrong. — Plochie
– Plochie, Commented Dec 23, 2019 at 4:44

Azad · Accepted Answer · 2019-12-23 04:35:50Z

2

you can import the class and refer the class property in you components.

assume you have your constant class in the const.class.ts file

import { CallTree } from './const.class'

export class AppComponent  {

  name = CallTree.active;    

}

answered Dec 23, 2019 at 4:35

Azad

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1 Comment

HK KNVB Over a year ago

Your answer inspired me to find the solution.

Chanaka Weerasinghe · Accepted Answer · 2019-12-23 04:38:54Z

0

You can declare like this

export class CallTree{

static readonly: number = 1;

}

https://www.tutorialsteacher.com/typescript/typescript-static

answered Dec 23, 2019 at 4:38

Chanaka Weerasinghe

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