CODEWITHSUNDEEP
javascriptangularjstypescriptangular-promise
Julia Leyton
Julia Leyton

Reputation: 13

Method executing on undefined result (from method with promises to resolve)

This could be (and probably is) a simple question, but I'm really confused with how to handle promises. I've been reading a lot about it, but still can't completely get it. I'm working with Typescript and Angular and I'm requesting data from an API REST. I have a method getServices, which returns an array with the information I get from the API.

My problem is when I call this method here:

this.getServices = (query) => {
            return this.source.getServices(query)
            .then(this.transformToSegments(false));
        };

I'm having an error TypeError: results is undefined.

results is used by transformToSegments. I put a lot of console.log() to debug and I saw that transformToSegments is executing before getServices gets resolved, so it tries to work on an undefined result. I'm obviously doing something wrong, but I haven't been able to fix it. Any help is appreciated!

Thanks in advance,

Julia

Upvotes: 1

Views: 67

Answers (1)

ktilcu
ktilcu

Reputation: 3128

This is a common mistake. You are passing the result of this.transformToSegments(false) to the .then() callback. I assume you want something more like:

.then(results => this.transformToSegments(false, results))

This will delay the execution of the transform until the then is called.

Upvotes: 2

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