Equal Sides Of An Array

findEvenIndex.js

// awesome
function findEvenIndex(arr)
{
  for(var i=1; i<arr.length-1; i++) {
    if(arr.slice(0, i).reduce((a, b) =>  a+b) === arr.slice(i+1).reduce((a, b) =>  a+b)) {
      return i;
    }
  }
  return -1;
}

// my 
function findEvenIndex(arr)
{		
	for (var i = 0; i < arr.length; i++) {
		var res_left = arr.reduce(function(sum, current, index) {
				return (index < i) ? (sum + current) : sum;
		}, 0);

		var res_right = arr.reduceRight(function(sum, current, index) {
				return (index > i) ? (sum + current) : sum;
		}, 0);
    
		if (res_left == res_right) {
			return  i;
		}
	}
	return -1; 
}