javascript - UserScript 根据按键采取行动？

Question

我正在努力尝试编写这个用户脚本的语法，它基本上应该遵循以下逻辑:

IF (LeftArrowKeyIsPressed) THEN doSomething;ELSE IF (RightArrowKeyIsPressed) THEN doSomethingElse;ELSE IF (any other key pressed) THEN doNothing;

有人可以帮我了解构造按键检查的代码语法吗？假设正在使用 onkeydown 事件。

Answer 1

使用 addEventListener 添加一个事件监听器，可能是到窗口。然后关闭 Event.which 值以执行您想要的操作。

这是代码。 See it in action at jsFiddle. :

/*--- Get or set the codes for the arrow keys.
    Firefox gives us nice constants, Chrome does not.
*/
KeyEvent        = (typeof KeyEvent === "object")  ?  KeyEvent  :  [];
const LEFT_KEY  = KeyEvent.DOM_VK_LEFT   ||  37;
const RIGHT_KEY = KeyEvent.DOM_VK_RIGHT  ||  39;

window.addEventListener ("keydown", keyboardHandler, false);

function keyboardHandler (zEvent) {
    var bBlockDefaultAction = false;

    //--- Assume we want only the plain keys, not the modified versions.
    if (zEvent.altKey  ||  zEvent.ctrlKey  ||  zEvent.shiftKey) {
        //-- Do nothing (most user-friendly option, in most cases).
    }
    else {
        if (zEvent.which == LEFT_KEY) {
            //DO LEFT KEY ACTION HERE.
            bBlockDefaultAction = true;
        }
        else if (zEvent.which == RIGHT_KEY) {
            //DO RIGHT KEY ACTION HERE.
            bBlockDefaultAction = true;
        }
    }

    if (bBlockDefaultAction) {
        zEvent.preventDefault ();
        zEvent.stopPropagation ();
    }
}

---

此代码适用于适用于用户脚本的浏览器(非 IE)。 jQuery 版本相同，只是将 addEventListener 行更改为:

$(window).keydown (keyboardHandler);