How to take keyboard input in JavaScript?

Solution 1:

You can do this by registering an event handler on the document or any element you want to observe keystrokes on and examine the key related properties of the event object.

Example that works in FF and Webkit-based browsers:

document.addEventListener('keydown', function(event) {
    if(event.keyCode == 37) {
        alert('Left was pressed');
    }
    else if(event.keyCode == 39) {
        alert('Right was pressed');
    }
});

DEMO

Solution 2:

You should register an event handler on the window or any element that you want to observe keystrokes on, and use the standard key values instead of keyCode. This modified code from MDN will respond to keydown when the left, right, up, or down arrow keys are pressed:

window.addEventListener("keydown", function (event) {
  if (event.defaultPrevented) {
    return; // Do nothing if the event was already processed
  }

  switch (event.key) {
    case "ArrowDown":
      // code for "down arrow" key press.
      break;
    case "ArrowUp":
      // code for "up arrow" key press.
      break;
    case "ArrowLeft":
      // code for "left arrow" key press.
      break;
    case "ArrowRight":
      // code for "right arrow" key press.
      break;
    default:
      return; // Quit when this doesn't handle the key event.
  }

  // Cancel the default action to avoid it being handled twice
  event.preventDefault();
}, true);
// the last option dispatches the event to the listener first,
// then dispatches event to window