How to fix "Uncaught TypeError: db.collection is not a function"?

Question

code in which the error occurs:

const countRef = db.collection('counter').doc('counter');
const increment = firebase.Firestore.FieldValue.increment(1);
const decrement = firebase.Firestore.FieldValue.increment(-1);
function change(num) {
    if (num>0) {
        countRef.update({ counter: increment });
    } else if (num<0) {
        countRef.update({ counter: decrement });
    };
};

The error is in the first line of code. I have also tried to search the internet for answers, but I have not yet found any.

Answer 1

_{As you haven't shown what db is defined to, this answer may be incorrect/not help.}

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The issue seems to be that you are setting db to an object which doesn't have collection().

Make sure that the db variable is defined and set to the following:

const db = firebase.firestore();

This object has the collection() method defined in it, which may fix the issue.