Understanding nested for loops in javascript

Question

I\'m learning JavaScript at the moment on freecodecamp and they have an example for nested for loops in one of their excercises:

 var arr = [[1,2], [3,4], [5,6]]         


        

Answer 1

I know this is an old question... But because this is a popular post from ye olde google search, I feel it's helpful to add a way to visualize what's going on in nested for-loops.

As a JS teacher, I've found this method super helpful for visually-oriented people and those w/ dyslexia and related things).

// Original: https://repl.it/@justsml/nested-loop-visualizations
var nums = [[1,2,3], [4,5,6], [7,8,9]];

console.log('Example w/ Numbers:\n');
console.log('The array data: ', JSON.stringify(nums));

for (var i=0; i < nums.length; i++) {
  // Main/"top" array - accessing via "arr[i]"
  for (var j=0; j < nums[i].length; j++) {
    // here we loop through the "child" arrays
    let helpfulLabel = `nums[${i}][${j}]`
    let value = nums[i][j]
    console.log(helpfulLabel, 'Value=' + value);
  }
}

console.log('\nExample w/ String Data:\n');
var letters = [['a', 'b', 'c'], ['d', 'e', 'f'], ['x', 'y', 'z']];
console.log('The array data: ', JSON.stringify(letters));

for (var i=0; i < letters.length; i++) {
  for (var j=0; j < letters[i].length; j++) {
    let helpfulLabel = `letters[${i}][${j}]`
    let value = letters[i][j]
    console.log(helpfulLabel, 'Value=' + value);
  }
}

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