JSFiddle - React, Tailwind, and code Playground

by joplomacedo

JavaScript

const prevBars=['b1', 'b2', 'b3'];
const newBars=['b1', 'b2', 'b3', 'b4', 'b5'];

function findLastIndex(arr, predicate = () => false ) {
    let l = arr.length;

    while (l--) {
      if ( predicate(arr[l], l, arr) ) {
        return l;
      }
    }

    return -1;
};

const  idx = findLastIndex( newBars, item => item == 'b2' );

console.log(idx);

console.log('common:', newBars.slice(0, idx+1))
console.log('new:', newBars.slice(idx+1))