Typescript | Calling a Function via Reference Does Not Work

Question

I am trying to call a function via reference. It all starts in callMe() of class DynamicCalls:

interface IDynamicFunction {
    name: string;
    func: (param: string) => void;
}

class DynamicCalls {

    private dynamicCall: IDynamicFunction = { name: "myDynamic", func: this.testFunc };

    public callMe() {
        this.callFromDynamic("Works"); // 1st -> Works
        this.testFunc("Works, also"); // 2nd -> Works
        this.dynamicCall.func("First Call"); // 3rd -> Error: callFromDynamic seems to be unknown in testFunc
    }

    private callFromDynamic(param: string): void {
        console.log("Param: " + param);
    }

    private testFunc(param: string): void {
        console.log("Param: " + param);
        this.callFromDynamic("Second call"); // Gives error -> TypeError: this.callFromDynamic is not a function
    }
}

let dynamicCalls: DynamicCalls = new DynamicCalls();

dynamicCalls.callMe();

I expect that the 3rd call (this.dynamicCall.func("First Call");) works like this.testFunc("Works, also").

Can anyone explain to me why I get this TypeError: this.callFromDynamic is not a function? And how I can avoid it?

Thanks a lot in advance.

Kind regards, Okean

Maxim Pyshko · Accepted Answer · 2019-08-25 11:49:24Z

2

The problem is that you lose the context.

In your case, this refers to the same object: {name: string, func: Function}

So you could work with:

private dynamicCall: IDynamicFunction = {
  name: "myDynamic",
  anotherFun: () => console.log('another func'),
  func: this.anotherFun()
};

Try:

private dynamicCall: IDynamicFunction = {
  name: "myDynamic",
  func: (param: string) => this.testFunc(param)
};

edited Aug 25, 2019 at 11:49

answered Aug 25, 2019 at 11:43

Maxim Pyshko

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Comments

Richard Haddad · Accepted Answer · 2019-08-25 16:35:29Z

0

@MaximP is right, but there is another solution.

    private callFromDynamic = (param: string): void => {
        console.log("Param: " + param);
    };

    private testFunc = (param: string): void => {
        console.log("Param: " + param);
        this.callFromDynamic("Second call");
    };

Change your functions to fields, now they'll keep their context without need to wrap their calls.

answered Aug 25, 2019 at 16:35

Richard Haddad

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