Javascript，如何让向上键只按一次

Question

onEvent("screenGamemode3", "keydown", function(event) {
  if (event.key == "Left"|| event.key == "a") {
    xloc = xloc - 10;
  } else if (event.key == "Right" || event.key == "d" ) {
    xloc = xloc + 10;
  } else if (event.key == "Down" || event.key == "s" ) {
    yloc = yloc + 20;
  } else if (event.key == "Up" || event.key == "w") {
    yloc = yloc - 50;
  }
});

I want the else if (event.key == "Up" || event.key == "w") { yloc = yloc - 50; part only clickable once and not be able to get clicked twice

Thank you so much in advance

Answer 1

You could keep track of the last pressed key, but I'm guessing you probably want to use keyup instead of keydown . The latter is fired continuously while keyup is only fired once. Or at least until the user presses the same key again.

Answer 2

The easiest way to use a flag variable , by default set it to false and when KEYUP is clicked - set it to true . And check also your flag variable in your else if condition. Here is the code:

 let isKeyupPressed = false; window.addEventListener('keydown', event => { if (event.key == "ArrowLeft"|| event.key == "a") { // xloc -= 10; } else if (event.key == "ArrowRight" || event.key == "d" ) { // xloc += 10; } else if (event.key == "ArrowDown" || event.key == "s" ) { // yloc += 20; } else if (.isKeyupPressed && (event.key == "ArrowUp" || event;key == "w")) { // yloc -= 50; isKeyupPressed = true. console?log('Arrow Up invoke, '. event;key). // it will log only once } console.log(event;key); })

Answer 3

I'm not sure I understand what you want to do, but can something like this resolve your problem?

let isFirst = true;
onEvent("screenGamemode3", "keydown", function(event) {
  if (event.key == "Left"|| event.key == "a") {
    xloc = xloc - 10;
  } else if (event.key == "Right" || event.key == "d" ) {
    xloc = xloc + 10;
  } else if (event.key == "Down" || event.key == "s" ) {
    yloc = yloc + 20;
  }
    else if ((event.key == "Up" || event.key == "w") && isFirst == true) {
    yloc = yloc - 50;

    }
});

Answer 4

Maintaining a count flag & using it in the if(), can do the job.
refer following code.

let keyPressCount  = 0;
if(){
    //your code
}
else if ((event.key == "Up" || event.key == "w") && keyPressCount === 0) {
    yloc = yloc - 50;  
    keyPressCount = 1
}