I'm making a game using canvas, and javascript.
When the page is longer than the screen (comments, etc.) pressing the down arrow scrolls the page down, and makes the game impossible to play.
What can I do to prevent the window from scrolling when the player just wants to move down?
I guess with Java games, and such, this is not a problem, as long as the user clicks on the game.
I tried the solution from: How to disable page scrolling in FF with arrow keys ,but I couldn't get it to work.
This question is related to
javascript
canvas
scroll
arrow-keys
I've tried different ways of blocking scrolling when the arrow keys are pressed, both jQuery and native Javascript - they all work fine in Firefox, but don't work in recent versions of Chrome.
Even the explicit {passive: false}
property for window.addEventListener
, which is recommended as the only working solution, for example here.
In the end, after many tries, I found a way that works for me in both Firefox and Chrome:
window.addEventListener('keydown', (e) => {
if (e.target.localName != 'input') { // if you need to filter <input> elements
switch (e.keyCode) {
case 37: // left
case 39: // right
e.preventDefault();
break;
case 38: // up
case 40: // down
e.preventDefault();
break;
default:
break;
}
}
}, {
capture: true, // this disables arrow key scrolling in modern Chrome
passive: false // this is optional, my code works without it
});
Quote for EventTarget.addEventListener()
from MDN
options Optional
An options object specifies characteristics about the event listener. The available options are:capture
ABoolean
indicating that events of this type will be dispatched to the registeredlistener
before being dispatched to anyEventTarget
beneath it in the DOM tree.
once
...
passive
ABoolean
that, if true, indicates that the function specified bylistener
will never callpreventDefault()
. If a passive listener does callpreventDefault()
, the user agent will do nothing other than generate a console warning. ...
For maintainability, I would attach the "blocking" handler on the element itself (in your case, the canvas).
theCanvas.onkeydown = function (e) {
if (e.key === 'ArrowUp' || e.key === 'ArrowDown') {
e.view.event.preventDefault();
}
}
Why not simply do window.event.preventDefault()
? MDN states:
window.event
is a proprietary Microsoft Internet Explorer property which is only available while a DOM event handler is being called. Its value is the Event object currently being handled.
Further readings:
Source: Stackoverflow.com