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How to Add Keyboard Shortcut Events Easily in JavaScript

Jul 27, 2020 2 min read

I was looking for an easy way to handle keyboard shortcuts in a web application I had been working on.

I wanted to register key presses like the following: ctrl+z, ctrl+shift+z, alt+x, m, etc.

While there are plenty of solid libraries out there for this (Mousetrap, HotKeys, etc.), I wanted to create my own shortcuts in vanilla JavaScript.

I decided to go with the keydown and keyup handlers in this scenario.

document.addEventListener("keydown", handleKeyDown);
document.addEventListener("keyup", handleKeyUp);

I needed to handle ctrl, shift, and alt keyboard shortcuts, so naturally, I needed some sort of “state” for these three keys. For that, I created isPressed.

let isPressed = {
  ctrl: false,
  shift: false,
  alt: false,
};

I could then update isPressed on each keydown and keyup event.

Then, on each non-ctrl, non-shift, and non-alt key, I print out the resulting key press combination.

const getCode = (e) => {
  e = e || window.event;
  return e.key;
};
const handleKeyDown = (e) => {
  e.preventDefault();
  const key = getCode(e);
  switch (key) {
    case "Control":
      isPressed.ctrl = true;
      break;
    case "Shift":
      isPressed.shift = true;
      break;
    case "Alt":
      isPressed.alt = true;
      break;
    default:
      const { ctrl, shift, alt } = isPressed;
      let pressed = "";
      if (ctrl) pressed += "ctrl+";
      if (shift) pressed += "shift+";
      if (alt) pressed += "alt+";
      pressed += key;
      console.log(pressed);
      break;
  }
};
const handleKeyUp = (e) => {
  e.preventDefault();
  const key = getCode(e);
  switch (key) {
    case "Control":
      isPressed.ctrl = false;
      break;
    case "Shift":
      isPressed.shift = false;
      break;
    case "Alt":
      isPressed.alt = false;
      break;
  }
};

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