Return first letter for each word in a given string

UppercasefirstLetterString.js

/**
 * First letter in uppercase of each word of a given string
 */
function UppercasefirstLetterString(str) {
  
	var arr = str.toLowerCase().split(' ');
  
  	return arr.map( function(letter) {
      
    		return letter[0].toUpperCase() + letter.slice(1);
    
  	}).join(' ');
 
}

// used
UppercasefirstLetterString("I'm a little tea pot");