Detect combination of user input using JavaScript

February 16, 2022

I’m trying to make an alert popup when I press a sequence of keys on my website, for example if I write "420" on my keyboard I want a message to popup saying "You made it" or something. I get it when I use only 2 keypresses using this:

  if (e.ctrlKey && e.keyCode == 90) {
    alert("Sweet");
  }
});

Which is the CTRL-key + letter Z, but I cant seem to understand how to make it work if I want it to be the correct sequence of 4 2 0 or something similar. And I’m only allowed to use JavaScript.

>Solution :

For that to work, you need to keep track of keys pressed.

Here, I add every key pressed to a variable str at that variable’s end, and then cut off everything except the last 3 characters.

let str = '';

window.addEventListener('keyup', function(event) {
  str = `${str}${event.key}`.substr(-3);
  if (str === '420') console.log('You made it!');
})