控制多个按键时出现奇怪的情况

Question

With the below code, when a key is pressed its keycode is pushed to the keymap array if it's not already there and when a key is let up its keycode is taken out of the array. When testing this out by constantly shoving the keymap array to the console, I found some strange things.

var keymap = [];

$(window).keydown(function(e) {
    if($.inArray(e.keyCode,keymap) == -1) {keymap.push(e.keyCode);}
});

$(window).keyup(function(e) {
    for(i = 0;i < keymap.length;i++) {
        if(keymap[i] = e.keyCode) {keymap.splice(i,1);}
    }
});

setInterval(function() {console.log(keymap);},100);

1. If I hold down a and d at the same time their keycodes are present in keymap, then if I hold down w all three of their keycodes are present. Now when I let go of w it's removed from the array, but so is d even though I'm still holding down d.

2. I then found that I can hold down a, w, and d and they'll all be put into keymap, but it will not put w, a, and s in keymap when I hold them down. A combination of two of these will be put in, but the third will not.

Can anyone tell me what's going on?

Answer 1

Your comparison is an assignment actually. Change if(keymap[i] = e.keyCode) to

if (keymap[i] == e.keyCode)
//             ^

Also, you should use local variables:

for(var i = 0; …
//  ^^^

And while it shouldn't matter for your array where items are supposed to be unique, you need to decrease the counter variable i after you remove an item or you skip to check the next one otherwise:

keymap.splice(i--,1)
//             ^^