Javascript For Loop: Assignment to character not working

Question

I was writing a test function to capitalize each word in a sentence. I ended up solving it; however, one of my first attempts to solve the problem didn't work when I thought it would.

function capSentence(str) { 
  var strArray = str.split(" ");
  var answer = '';
  var temp = '';
  for(var i = 0; i < strArray.length; i++){
    strArray[i][0] = strArray[i][0].toUpperCase();
    answer += strArray[i];
    if(i !== strArray.length-1){
      answer += ' ';
    }
  }
  return answer; 

}

capSentence("this is a test");

I thought the above code would output "This Is A Test", but instead it outputs "this is a test".

strArray[i][0] = strArray[i][0].toUpperCase();

doesn't seem to have any affect. Why is that?

http://stackoverflow.com/questions/4878756/javascript-how-to-capitalize-first-letter-of-each-word-like-a-2-word-city — Klemen Tusar, May 20 '14 at 13:41

score 1 · Accepted Answer · answered May 20 '14 at 13:54

@thefourtheye's comment is correct. You need to build a new string.

function capSentence(str) { 
  var strArray = str.split(" ");
  var answer = '';
  var temp = '';

  for(var i = 0; i < strArray.length; i++){
      answer += strArray[i][0].toUpperCase();
      answer += strArray[i].slice(1,strArray[i].length);

      if(i !== strArray.length-1){
        answer += ' ';
      }
   }

   return answer;

}

score 0 · Answer 2 · answered May 20 '14 at 13:49

Strings are immutable in Javascript. That's why you are not able to change the value of the strArray.

But you can do in this way:

function capSentence(str) { 
  strArray = str.split(" ");
  console.log(strArray);
  var answer = '';
  var temp = '';
  for(var i = 0; i < strArray.length; i++){

    for (var j = 0; j< strArray[i].length; j++) {
       if(j==0) {
          temp = strArray[i][j].toUpperCase();
       }  else {
         temp+=strArray[i][j];
       }
    }

    answer += temp;
    if(i !== strArray.length-1){
      answer += ' ';
    }
  }
  return answer; 

}

This will retrun "This Is A Test"

score 0 · Answer 3 · answered May 20 '14 at 13:52

Try this simple snippet,

function capSentence(str) {
 var strArray = str.split(" ");
 var answer = '';
 var temp = '';
 for(var i = 0; i < strArray.length; i++){
  answer += (strArray[i].substring(0,1)).toUpperCase()+strArray[i].substring(1);
  if(i !== strArray.length-1){
   answer += ' ';
  }
 }
 return answer;
}

Javascript For Loop: Assignment to character not working

3 Answers3