arrays - Why can't I swap characters in a javascript string?

Question

I am trying to swap first and last characters of array.But javascript is not letting me swap. I don't want to use any built in function.

function swap(arr, first, last){
    var temp = arr[first];    
    arr[first] = arr[last];
    arr[last] = temp;
}

Answer 1

Because strings are immutable.

The array notation is just that: a notation, a shortcut of charAt method. You can use it to get characters by position, but not to set them.

So if you want to change some characters, you must split the string into parts, and build the desired new string from them:

function swapStr(str, first, last){
    return str.substr(0, first)
           + str[last]
           + str.substring(first+1, last)
           + str[first]
           + str.substr(last+1);
}

Alternatively, you can convert the string to an array:

function swapStr(str, first, last){
    var arr = str.split('');
    swap(arr, first, last); // Your swap function
    return arr.join('');
}