Restricting input to only letters when using the onkeyup function and preventing keys like PgUp, Del, and ArrowLeft from being entered

I'm completely new to Javascript and for my assignment, I have been tasked with developing a letter guessing game. Although I've completed most of it, I wanted to take things a step further by incorporating an alert when anything other than a letter is pressed. I came across this helpful example just recently...

toLowerCase() != key.toUpperCase()

Yet, the input still includes arrow keys along with the six keys above them. Despite using onkeyup to return a string for these, I am struggling to isolate them using charAt(1). It doesn't seem to be working as intended.

function isLetter(key) {
  if (key.toLowerCase() != key.toUpperCase() && key.charAt(1) === '') {
    return true;
  } else {
    return false;
  }
}

Additionally, here is the keyup function:

document.onkeyup = function(event) {
  keyPress = event.key;
  if (!isLetter(keyPress)) {
    return alert('Please only enter letters');
  }
}

Answer №1

There may be a potential bug in your method. It's important to note that using the keys - and +, among others, will also pass the test.

A better approach would be to utilize a regular expression for testing the key stroke:

function validateKey(key) {
// Regular expression to check if the key is a single character from 'a' to 'z'
return key.match(/^[a-z]$/);
}

document.onkeyup = function (event) {
keyPressed = event.key;
if (!validateKey(keyPressed)) {
return alert('Please enter a letter');
}
}

Answer №2

To properly handle input symbols, it is important to utilize the direct code of each symbol. For more information, you can refer to this link: https://developer.mozilla.org/en-US/docs/Web/API/KeyboardEvent/keyCode

const ACode = 65;
const ZCode = 90;
function checkIfLetter(key) {
    return ACode <= key && key <= ZCode;    
}

document.onkeyup = function (event) {
    keyPressed = event.keyCode;
    if (!checkIfLetter(keyPressed)) {
        return alert('Please enter a letter');
    }
}

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