First letter of each word in capital

JavaScript
1 
function titleCase(str) {
  str = str.toLowerCase().split(" ");
  for(var i=0;i<str.length;i++){
    str[i]= str[i].split("");
    str[i][0] = str[i][0].toUpperCase();
    str[i]=str[i].join("");
  }
  return str.join(" ");
}

This is the code I wrote for the uppercase challenge. I used a little more lines I think but this makes me understand better. I first wrote the code like below

function titleCase(str) {
  str = str.toLowerCase().split(" ");
  for(var i=0;i<str.length;i++){
    str[i]= str[i].charAt(0).toUpperCase()+str[i].substring(1);
  }
  return str.join(" ");
}

What is the difference between these two, both run fine and give the same result. I think the difference is in the run time of the two. A little bit more light on this would be great. Thanks!

2

The first one has more operations chained together. One of the powerful features of JS.
But yes, the second one is a bit more readable.