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('');
}

Answer 2

Let me offer my side of what I understood: swapping items of an array could be something like:

var myFish = ["angel", "clown", "mandarin", "surgeon"];
var popped = myFish.pop();
myFish.unshift(popped) // results in ["surgeon", "angel", "clown", "mandarin"]

Regarding swaping first and last letters of an strings could be done using Regular Expression using something like:

"mandarin".replace(/^(\w)(.*)(\w)$/,"$3$2$1")// outputs nandarim ==> m is last character and n is first letter

Answer 3

I just ran your code right out of Chrome, and it seemed to work find for me. Make sure the indices you pass in for "first" and "last" are correct (remember JavaScript is 0-index based). You might want to also try using console.log in order to print out certain variables and debug if it still doesn't work for you.

EDIT: I didn't realize you were trying to manipulate a String; I thought you just meant an array of characters or values.