gasstation.cpp https://leetcode.com/problems/gas-station/ | my solution in javascript

gasstation.js

/**
 * @param {number[]} gas
 * @param {number[]} cost
 * @return {number}
 */
var canCompleteCircuit = function(gas, cost) {
  let start=0, gasLeft=0, sum=0; // left-gas left in the tank
  
    for (let i=0; i<gas.length; i++) {
        gasLeft+= gas[i] - cost[i];
        sum+= gas[i] - cost[i];
        if (sum<0) {
            sum=0;
            start=i+1;
        }
    }
    return gasLeft<0 ? -1: start;
}