Function For Adding Space Between Characters Not Working

I'm trying to write a function that takes a word and adds a space between each letter e.g space becomes s p a c e. I have written below but when I call the function it says the argument is not defined.

Code:
function insertSpaces(string){
var currentCharacter;
var resultString;
resultString = ''
//a line to loop through each charcther in the string agument
for (var position = 0; position < string.length; position =
position + 1){
// set current characther as the first charcter in the string and add a space
currentCharacter = (string.charAt(position) + ' ')
//store the currentcharcter and add followng characthers
resultString = currentCharacter + resultString
} return resultString
}