Caesar cipher error

JavaScript
#1

Bit stuck, why am I getting this error - Cannot assign to read only property ‘1’ of string ‘serr’



function rot13(str) { // LBH QVQ VG!
    	var alphabet = ['a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z']
  	var wordsLC = str.toLowerCase();
  	var words = wordsLC.split(' ');
        var wordStr = "";
  		

  		for(var i = 0;i<words.length;i++){
  			
  			var wordLetters = words[i];
  			console.log("Word: " + wordLetters);


  			for(var j=0;j<wordLetters.length;j++) {
  				var patt = /[^a-zA-Z]/g;
                var pattCheck = patt.test(wordLetters[j]);

                if(pattCheck == true){ 
                	wordStr += wordLetters[j];
                	continue;
                }

	  			var jcount = alphabet.indexOf(wordLetters[j]);
	  			
                jcount += 13;
            

	  			if(jcount >25){
	  				jcount = jcount -26;
	  				wordStr += alphabet[jcount]

	  			}
	  			else{
	  				wordLetters[j] = alphabet[jcount]
	  				wordStr += alphabet[jcount]
	  			}
  		    }

  		    
  			words[i] = wordStr;
  			wordStr = "";
  		
  		}
        var wordsDone = words.join(" ");
       
  		return wordsDone.toUpperCase();
	}
#2

I’ve edited your post for readability. When you enter a code block into a forum post, please precede it with a separate line of three backticks and follow it with a separate line of three backticks to make easier to read.

See this post to find the backtick on your keyboard. The “preformatted text” tool in the editor (</>) will also add backticks around text.

Note: Backticks are not single quotes.

markdown_Forums

#3

Will do many thanks for your help

#4

Not sure if you figured out the issue with your code. The reason your code produces that error is because behind the scenes, FCC uses "use strict"; which will cause certain errors to show that would normally fail silently. In your case, in the following line:

wordLetters[j] = alphabet[jcount]

you are attempting to mutate a string, which is not possible in JavaScript. You can assign a new value to a string variable, but you can not change individual characters as you are trying to do. If you just remove this line all together, your remaining code allows you to produce a successful solution.

1 Like
#5

Thank you very much Randell, I totally forgot about strings not being mutable (Doh!).
Much appreciated

#6