如何在输入元素之外使用 onkeydown？

Question

我在一个JS中有积分canvas。我点击它们来启动不同的功能。我已经在使用右键和左键单击，但如果我在左键单击时按下 SHIFT，我想做一些不同的事情。

我需要检测onkeydown，但光标不在输入元素中。我该怎么做？

例如：

function getPosition3(event) // to get click position in canvas3
{   var canvas = document.getElementById("canvas3");
    mousePos = getMousePos(canvas, event); 
    ge3.px = mousePos.x;
    ge3.py = mousePos.y;
    p2g(ge3);       // converts pixels to graphic coordinates ge3.gx & ge3.gy
    closestDist = 5000000;
    chn = -1; // will contain index of the closest hedge to the click
    [nearestX, nearestY, chn] = nearestHedge(ge3.gx, ge3.gy);
    rnddot(ge3, nearestX, nearestY, 4, '#000000', 0);

    if (event.which==3) {popit(chn);} //popup graph on right click 
    else {poptxt(chn);} 
// Here I'd like to detect onkeydown to allow another option

}

Answer 1

使用 window.addEventListener("keydown/keyup", ...) 将 keydown 和 keyup 事件附加到 window 并保留一个跟踪 shift 键按下状态的全局变量。

然后在 getPosition3 函数中检查那个变量。

var shiftPressed = false;
window.addEventListener("keydown", function(ev) {
    shiftPressed = ev.shiftKey; // or whatever property. Just written on-the-fly and I'm not sure if is shiftKey.
});
window.addEventListener("keyup", function(ev) {
    shiftPressed = ev.shiftKey;
});

function getPosition3(event) {
    // [...]
    // blah blah
    // [...]
    if (shiftPressed) {
        // Things
    }
}

Answer 2

香草味 javascript:

var shiftPressed = false;

document.addEventListener ('keydown', function(event) {
  shiftPressed = event.shiftKey;
});

document.addEventListener ('keyup', function(event) {
  shiftPressed = event.shiftKey;
});

然后改变你的功能：

if (shiftPressed) {popit(chn);}

JS Fiddle: https://jsfiddle.net/charlesartbr/6L4juxbk/

如何在输入元素之外使用 onkeydown？

How can I use onkeydown outside of an input element?

javascript

onkeydown