Call javascript method variable loses 'this'

Question

I've created a simple pointer to a method like so:

export class SmbwaService {
    getExistingArsByLab(labId: number): Observable<SmwbaAr[]> {
        this.otherMethod();
    }

    otherMethod(): void {
    }
}


let method: (x: number) => Observable<SmbwaAr[]>;
method = this.service.getExistingArsByLab;
method(12);

That executes OK insofar as it does call getExistingArsByLab method. However, I then get an error when it tries to call otherMethod because:

Cannot read property otherMethod of undefined.

What's the right way to do this? Obviously in my actual code method is being set to one of a number of different methods based on some conditions.

I'm assuming the last 3 lines of code in your example are actually inside of another class where you set `service = new SmbwaService()`, right? — Chris Barr, May 11 '18 at 17:14
Keep in mind that `this` in JavaScript vs.`this` in a Typescript class are two entirely different things. — Chris Barr, May 11 '18 at 17:58

score 2 · Answer 1 · answered May 11 '18 at 17:11

2

Use Function.bind to obtain a function reference that's bound to a particular value of this:

method = this.service.getExistingArsByLab.bind(this.service)
method(2)

answered May 11 '18 at 17:11

jspcal

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Call javascript method variable loses 'this'

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