Finding the index position of an array inside an array JavaScript

When working with arrays of arrays in JavaScript, you might need to find the index position of a specific sub-array within the main array. This is useful for checking if a particular array exists and determining its location.

Suppose we have an array of arrays like this:

const arr = [
   [1,0],
   [0,1],
   [0,0]
];

We need to write a JavaScript function that takes an array of arrays as the first argument and a target array as the second argument. The function should return the index position of the target array if it exists, or -1 if it doesn't.

Using Array Methods with Helper Function

const arr = [ [1,0], [0,1], [0,0] ];
const sub = [0, 0];

const matchEvery = (arr, ind, sub) => arr[ind].every((el, i) => el == sub[i]);

const searchForArray = (arr = [], sub = []) => {
   let ind = -1;
   let { length: len } = arr;
   
   while (len--) {
      if (arr[len].length === sub.length && matchEvery(arr, len, sub)) {
         ind = len;
         break;
      }
   }
   return ind;
};

console.log(searchForArray(arr, sub));

2

Using findIndex() Method

A more modern and concise approach uses the findIndex() method:

const arr = [ [1,0], [0,1], [0,0] ];
const sub = [0, 0];

const findArrayIndex = (arr, target) => {
   return arr.findIndex(subArray => 
      subArray.length === target.length && 
      subArray.every((val, index) => val === target[index])
   );
};

console.log(findArrayIndex(arr, sub));
console.log(findArrayIndex(arr, [1, 0]));
console.log(findArrayIndex(arr, [2, 3])); // Not found

2
0
-1

Using JSON.stringify() for Simple Arrays

For arrays containing only primitive values, you can use JSON.stringify() for comparison:

const arr = [ [1,0], [0,1], [0,0] ];
const sub = [0, 0];

const findIndexWithStringify = (arr, target) => {
   const targetString = JSON.stringify(target);
   return arr.findIndex(subArray => JSON.stringify(subArray) === targetString);
};

console.log(findIndexWithStringify(arr, sub));
console.log(findIndexWithStringify(arr, [0, 1]));

2
1

Comparison of Methods

Conclusion

The findIndex() method with every() provides the best balance of readability and performance for finding array indices. Use JSON.stringify() only for simple primitive arrays where order matters.