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JavaScript JavaScript Loops, Arrays and Objects Tracking Multiple Items with Arrays Two-Dimensional Arrays

Vic Mercier
Vic Mercier
3,276 Points
Posted by Vic Mercier
Vic Mercier
3,276 Points

Problem...

1.I'd like to make a little quizz game but instead of t the question are already there(in the 2 dimensional array)I want to capture by a prompt dialog then add them to my two dimensinal array. var question = [ [], [] ]; var lol; for(var i = 0; i < question.length; i += 1){ lol = prompt("Please type a question"); question[i][0].push(lol); }

The promblem is that the loop cannnot run more than one time.It just run once and the queston.length is 2 so the loop should run two times because i was set to zero.

Victor

Thank you for your help!

2 Answers

andren
andren
28,558 Points
andren
andren
28,558 Points

It technically does not even loop once, it stops once it encounters this line:

question[i][0].push(lol);

If you look at the console after running that command you will see this:

TypeError: Cannot read property 'push' of undefined

The issue is the [0] part of that line, it does not belong there. The [i] tells JavaScript to retrive the i element of the array, which at first will be the first nested array. Then the [0] tells it to retrieve the first element of that array, which does not exist since the nested array is empty. Hence the error.

The push method should be called directly on the nested array, so by removing the [0] like this:

var question = [ [], [] ];
var lol;
for(var i = 0; i < question.length; i += 1){
  lol = prompt("Please type a question");
  question[i].push(lol);
}

console.log(question)

Your code will function in the way I'm guessing you intended it to.

Vic Mercier
Vic Mercier
3,276 Points
Vic Mercier
Vic Mercier
3,276 Points

But could do we add an element in a precise place in a two dimensional Arras?

Brennan Altringer
Brennan Altringer
7,660 Points

You can add a value to a 2D array in a specific spot. But in your loop 0 is static so I'm not sure you need a 2D array. You could use a singular array and achieve the same results based on your code above.

if you wanted a 2d array you would need a nested for loop like so:

var question = [ [], [] ];
var lol;
   for(var i = 0; i < question.length; i ++){
     for(var j = 0; j < question.length; j ++){
        lol = prompt("Please type a question");
        question[i][j].push(lol);
   }
}

console.log(question)

If that what you are looking for?