javascript - For loop - Uncaught TypeError: str[i] is undefined - why?

Question

I'm doing a caeser code exercise and have run into an issue very early on, which seems to be mistifying me. Any help would be appreciated! Here's my code:

const caesar = function(str, number) {

    let solved = "";

  for (let i = 0; i <= str.length; i++) {

     let asciiNum = str[i].charCodeAt();

     if (asciiNum >- 65 && asciiNum <= 90) {
       solved += String.fromCharCode(asciiNum + number);
     }
  }
};

The error:

Uncaught TypeError: str[i] is undefined
    caesar http://127.0.0.1:5501/index.html:102
    <anonymous> debugger eval code:1

why is str[i] undefined? I'm hella confused!

Answer 1

Rewrite your for loop as below:

for (let i = 0; i < str.length; i++) {}

It must be i < str.length otherwise, during the last iteration, str[i] will resolve to undefined.