JSFiddle - React, Tailwind, and code Playground

JavaScript

function getIndexOf(array, x) {
  for (var i = 0; i < array.length; i++) {
    for (j=0; j<array[0].length;j++){
    var k = array[i][j].indexOf(x); 
    if (k > -1) {
        return [i, j, k];
    }
  }
 }
}

var arr=new Array();
arr[0]=new Array();
arr[0][0]=new Array();
arr[0][0][0]=2;
arr[0][0][1]=3;

alert(getIndexOf(arr,3));