How to get all substrings (contiguous subsequences) of my JavaScript array?

Question

My task is to split the given array into smaller arrays using JavaScript. For example [1, 2, 3, 4] should be split to [1] [1, 2] [1, 2, 3] [1, 2, 3, 4] [2] [2, 3] [2, 3, 4] [3] [3, 4] [4].

I am using this code:

let arr = [1, 2, 3, 4];

for (let i = 1; i <= arr.length; i++) {
  let a = [];
  for (let j = 0; j < arr.length; j++) {
    a.push(arr[j]);
    if (a.length === i) {
      break;
    }
  }
  console.log(a);
}

And I get the following result: [1] [1, 2] [1, 2, 3] [1, 2, 3, 4] undefined

What am I missing/doing wrong?

Answer 1

For the inner array, you could just start with the index of the outer array.

var array = [1, 2, 3, 4],
    i, j, l = array.length,
    result = [];
    
for (i = 0; i < l; i++) {
    for (j = i; j < l; j++) {
        result.push(array.slice(i, j + 1));
    }
}
console.log(result.map(a => a.join(' ')));

.as-console-wrapper { max-height: 100% !important; top: 0; }

Answer 2

You have two issues in your code:

1. You need to have loop to initialize with the value of i for the inner loop so that it consider the next index for new iteration of i
2. You need to remove that break on the length which you have in inner loop.

let arr = [1, 2, 3, 4];
for (let i = 0; i <= arr.length; i++) {
  let a = [];
  for (let j = i; j < arr.length; j++) {
    a.push(arr[j]);
    console.log(a);
  }
}

Answer 3

Try this

 let arr = [1, 2, 3, 4];
       for (let i = 0; i <= arr.length; i++) {
          let a = [];
          for (let j = i; j < arr.length; j++) {
            a.push(arr[j]);    
              console.log(a);            
          }  
        }