gistfile1.txt

function replace(str, before, after) {
 var arr = str.split(" ")
 var newArr = []
 
 
 for(i=0;i<arr.length;i++){
   if (arr[i]==before){
     if(before.charAt(0).toUpperCase()){
         after.split("")[0]=after.charAt(0).toUpperCase()
         newArr.push(after)
     }
     }else{  
     newArr.push(arr[i])
   } 
   
   var newStr = newArr.join(" ") 
 }
  return newStr
}
replace("A quick brown fox jumped over the lazy dog", "jumped", "leaped");