禁用用户浏览器中的箭头键滚动

我在用画布和 javascript 做一个游戏。

当页面长于屏幕(评论等)时,按下箭头向下滚动页面,使游戏无法进行。

当玩家只是想向下移动时,我该怎么做才能防止窗口滚动?

我猜对于 Java 游戏来说,这不是问题,只要用户点击游戏。

我尝试了解决方案从: 如何使用箭头键禁用 FF 中的页面滚动,但我不能得到它的工作。

131092 次浏览

Summary

Simply prevent the default browser action:

window.addEventListener("keydown", function(e) {
if(["Space","ArrowUp","ArrowDown","ArrowLeft","ArrowRight"].indexOf(e.code) > -1) {
e.preventDefault();
}
}, false);

If you need to support Internet Explorer or other older browsers, use e.keyCode instead of e.code, but keep in mind that keyCode is deprecated and you need to use actual codes instead of strings:

// Deprecated code!
window.addEventListener("keydown", function(e) {
// space and arrow keys
if([32, 37, 38, 39, 40].indexOf(e.keyCode) > -1) {
e.preventDefault();
}
}, false);

Original answer

I used the following function in my own game:

var keys = {};
window.addEventListener("keydown",
function(e){
keys[e.code] = true;
switch(e.code){
case "ArrowUp": case "ArrowDown": case "ArrowLeft": case "ArrowRight":
case "Space": e.preventDefault(); break;
default: break; // do not block other keys
}
},
false);
window.addEventListener('keyup',
function(e){
keys[e.code] = false;
},
false);

The magic happens in e.preventDefault();. This will block the default action of the event, in this case moving the viewpoint of the browser.

If you don't need the current button states you can simply drop keys and just discard the default action on the arrow keys:

var arrow_keys_handler = function(e) {
switch(e.code){
case "ArrowUp": case "ArrowDown": case "ArrowLeft": case "ArrowRight":
case "Space": e.preventDefault(); break;
default: break; // do not block other keys
}
};
window.addEventListener("keydown", arrow_keys_handler, false);

Note that this approach also enables you to remove the event handler later if you need to re-enable arrow key scrolling:

window.removeEventListener("keydown", arrow_keys_handler, false);

References

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:

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
   A Boolean indicating that events of this type will be dispatched to the registered listener before being dispatched to any EventTarget beneath it in the DOM tree.
once
   ...
passive
   A Boolean that, if true, indicates that the function specified by listener will never call preventDefault(). If a passive listener does call preventDefault(), the user agent will do nothing other than generate a console warning. ...

This is the accepted answer rewritten for React.

import { useEffect } from "react";


const usePreventKeyboardScrolling = () => {
const onKeyDown = (e) => {
if (
["Space", "ArrowUp", "ArrowDown", "ArrowLeft", "ArrowRight"].indexOf(
e.code
) > -1
) {
e.preventDefault();
}
};


useEffect(() => {
window.addEventListener("keydown", onKeyDown, false);
return () => window.removeEventListener("keydown", onKeyDown);
});
};


export { usePreventKeyboardScrolling };