How to alternate the case of a string

Question

I'm working on alternating the case of a string (for example asdfghjkl to AsDfGhJkL). I tried to do this. I found some code that is supposed to do it, but it doesn't seem to be working.

var str="";

var txt=document.getElementById('input').value;

for (var i=0; i<txt.length; i+2){
    str = str.concat(String.fromCharCode(txt.charCodeAt(i).toUpperCase()));
}

Answer 1

Here's a quick function to do it. It makes the entire string lowercase and then iterates through the string with a step of 2 to make every other character uppercase.

var alternateCase = function (s) {
  var chars = s.toLowerCase().split("");
  for (var i = 0; i < chars.length; i += 2) {
    chars[i] = chars[i].toUpperCase();
  }
  return chars.join("");
};

var txt = "hello world";
console.log(alternateCase(txt));

HeLlO WoRlD

The reason it converts the string to an array is to make the individual characters easier to manipulate (i.e. no need for String.prototype.concat()).

Answer 2

Here an ES6 approach:

function swapCase(text) {
    return text.split('').map((c,i) => 
        i % 2 == 0 ? c.toLowerCase() : c.toUpperCase()
    ).join('');   
}

console.log(swapCase("test"))