Conditionally adding a property in TypeScript

Question

I'd like to conditionally add a property to an object (or maybe I mean a class - I am unsure of the actual semantics in TypeScript).

import IMetadata from './metadata-interface';

export default class MetaData {

    [idx: string]: IMetadata;

    public 'foo' = {
        name: 'foo',
    } as IMetadata;

    public 'bar' = {
        name: 'bar',
    } as IMetadata;
};

But how do I conditionally add bar to the object? Can I do something like:

export default class MetaData {

    [idx: string]: IMetadata;

    public 'foo' = {
        name: 'foo',
    } as IMetadata;

    if(condition) {
      public 'bar' = {
          name: 'bar',
      } as IMetadata;
    }
};

"or maybe I mean a class". What's your goal here? Class and object are the same concepts like in other class-based languages. Do you really want to have conditional logic in constructing a class definition? — Alex
– Alex, Commented Nov 17, 2016 at 20:00
"Do you really want to have conditional logic in constructing a class definition?" Yes. I come from JavaScript (I am quite experienced with it). I am a total beginner with TypeScript. — Ben Aston
– Ben Aston, Commented Nov 17, 2016 at 20:01
I'm quite sure this is not possible, but could you elaborate on your use-case? I'm not totally convinced that you are actually looking for something like C# preprocessor directives here :) — Alex
– Alex, Commented Nov 17, 2016 at 20:07
So as you accepted Ryans answer, I guess you wanted to add a property to an object through a class definition and that you didn't mind the class always having that property defined as optional. — Alex
– Alex, Commented Nov 17, 2016 at 20:24

Ryan Cavanaugh · Accepted Answer · 2016-11-17 20:07:01Z

4

Use an if statement:

export default class MetaData {

    [idx: string]: IMetadata;

    public 'foo' = {
        name: 'foo',
    } as IMetadata;

    public 'bar'?: IMetadata;

    constructor(condition: boolean) {
        if (condition) {
            this.bar = {
                name: 'bar',
            };
        }
    }
}

answered Nov 17, 2016 at 20:07

Ryan Cavanaugh

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