Javascript Custom Reduce function

var arr = [4,2,5,3];


function myRd(arr,callback){

	var val=arr[0];
	for(i=1;i<arr.length;i++){
  	val = callback(val,arr[i]);  
  }
  return val;
}
var x = myRd(arr,function(a,b){
	return a+b;
})

console.log(x);