Boolean function returning undefined in javascript?

Question

I currently am using data stored in Firebase to check if a user-submitted solution is correct. This involves me calling the function getSolutionAndCompare when the user presses a “submit” button. However, for some reason, although checkSolution is returning true to getSolutionAndCompare, when I call getSolutionAndCompare in onSubmitPressed, it evaluates as undefined. Any idea what I could be doing wrong?

Relevant code:

onSubmitPressed: function() {
    var output = this.getSolutionAndCompare();
    console.log('output ' + output); //this is returning undefined
    if (this.getSolutionAndCompare()) {
        Alert.alert(
            'Correct',
            "Woohoo!"
        );
    }
    else {
        Alert.alert(
            'Incorrect Submission',
            'Try again!',
        );
    }
},

getSolutionAndCompare: function() {
    var databaseSolution;
    solutionsRef.orderByChild('question_id').equalTo(Number(this.props.questionId)).once('value', (snap) => {
        var solution = snap.val();
        for (var key in solution) {
            databaseSolution = solution[key].solution;
        }
        return this.checkSolution(databaseSolution); //checkSolution returns true here
    });

},

checkSolution: function(databaseSolution) {
    if (this.state.submission == databaseSolution) {
        return true;
    }
    else {
        return false;
    }
},

What kind of data are you expecting to be in held in `solution` here? `var solution = snap.val()`? You go on to iterate over the `solution` object but you're only checking the final value in your return statement. Edit - that return statement doesn't appear to be returning the `getSolutionAndCompare` method so that method returns `undefined` — bcr, May 23 '16 at 14:57
`solutionsRef.orderByChild('question_id').equalTo(Number(this.props.questionId)).once('value', (snap) => {` -- is this an async call? Either way, you are returning inside of an inner function, which isn't what you want. — Jeremy J Starcher, May 23 '16 at 14:58

score 3 · Accepted Answer · edited May 23 '17 at 12:22

3

getSolutionAndCompare doesn't have a return statement, so it returns undefined because that is the default.

(The anonymous arrow function you declare inside getSolutionAndCompare has a return statement, but that looks asyncronous so you can't return its value).

edited May 23 '17 at 12:22

Community

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answered May 23 '16 at 14:57

Quentin

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Boolean function returning undefined in javascript?

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