Q:

Array from firebase database call logs correct data but length shows 0

I am making a call to the database and grabbing each of the map items from an array and storing them in an array that I am returning. The array shows the correct data if I log to the console but the array seems to be empty when I try to reference any of the data and the length of the array is also zero. 
$(document).ready(function(){
    //This ('click','li') binds all dynamically added shit to respond to click.
    $('ul.hiddentext').on('click','li', function(e){
        $(this).siblings().css('font-weight','normal');
        $(this).css('font-weight','bolder');
        let text = $(this).text();
        currentWorkoutSelected = text;
        var exercises = pullWorkoutTableData(text)
        console.log(exercises.length);
        var workout = new workoutTemplate(text, user, exercises);
        workout.populateTable();

        //Populate the title of the workout based on if its already there or not.
        if($('h4#workoutTitle').length == 0){
            $("table.exerciseList").prepend('<h4 id="workoutTitle">'+ text+ '</h4>');
        }
        else{
            $('h4#workoutTitle').replaceWith('<h4 id="workoutTitle">'+ text+ '</h4>');
        };
    });
});

//Taking the data needed for the workout table from the database.
function pullWorkoutTableData(workoutName){
    var exerciseList = [];
    db.collection('workouts').get().then((snapshot)=>{
        snapshot.docs.forEach(doc => {
            if(doc.data().name === workoutName && doc.data().user.includes(user)){
                doc.data().exercises.forEach(element =>{
                    var exercise = [element.name, element.weight, element.reps];
                    exerciseList.push(exercise);
                });
            };
        });
    });
    console.log(exerciseList);
    this.setState({exerciseList});
    return exerciseList;
};

Expecting to be able to call the populateTable function but the object isnt created correctly because the array is empty.

A:

Problem is db.collection returns a promise, and the data is not yet available when you log it.
you can try a couple of things here:
Move your set state into the listener, if you only care about the React state
function pullWorkoutTableData(workoutName){
    var exerciseList = [];
    db.collection('workouts').get().then((snapshot)=>{
        snapshot.docs.forEach(doc => {
            if(doc.data().name === workoutName && doc.data().user.includes(user)){
                doc.data().exercises.forEach(element =>{
                    var exercise = [element.name, element.weight, element.reps];
                    exerciseList.push(exercise);
                });
            };
        });
        this.setState({exerciseList}); // <---- HERE
    });

    return exerciseList;
};

Another thing you can do is to use an async/await function, but probably to update the state is enough for your case :)
If you browser support it.
function pullWorkoutTableData(workoutName){
    var exerciseList = [];
    return db.collection('workouts').get().then((snapshot)=>{
        snapshot.docs.forEach(doc => {
            if(doc.data().name === workoutName && doc.data().user.includes(user)){
                doc.data().exercises.forEach(element =>{
                    var exercise = [element.name, element.weight, element.reps];
                    exerciseList.push(exercise);
                });
            };
        });
        return Promise.resolve({ exerciseList })
    });
};
$(document).ready(async function(){
    //This ('click','li') binds all dynamically added shit to respond to click.
    $('ul.hiddentext').on('click','li', function(e){
        $(this).siblings().css('font-weight','normal');
        $(this).css('font-weight','bolder');
        let text = $(this).text();
        currentWorkoutSelected = text;
        var { exerciseList: exercises } = await pullWorkoutTableData(text)
        console.log(exercises.length);
        var workout = new workoutTemplate(text, user, exercises);
        workout.populateTable();

        //Populate the title of the workout based on if its already there or not.
        if($('h4#workoutTitle').length == 0){
            $("table.exerciseList").prepend('<h4 id="workoutTitle">'+ text+ '</h4>');
        }
        else{
            $('h4#workoutTitle').replaceWith('<h4 id="workoutTitle">'+ text+ '</h4>');
        };
    });
});

