JavaScript if 语句突然停止工作

Question

I am making a pong project right now, and I have a bit of code that lets changing directions be more smooth, so when you press both keys at the same time it won't freeze up for a moment. This happens in the up() function below.

let rx = 0;

pressDown = 
document.addEventListener('keydown', down);

pressUp = 
document.addEventListener('keyup', up);

function down(){
  if(event.keyCode === 39){
    rx = 3;

  }
  if(event.keyCode === 37){
    rx = -3;
  }
}
function up(){
  if (rx < 0 && event.keyCode === 37){
    rx = 0;
  }
  if (rx > 0 && event.keyCode === 39){
    rx = 0;
  }
}

It was working fine the other day, but when I opened my project this morning, this if statement suddenly did not work. The first part of the code does not work either until I change the second one by removing the rx < 0 and rx > 0 . I tried switching the < and > as well, but it did nothing. Does anyone have an answer or a solution?

Answer 1

Looks like there are a few problems with your implementation:

1. You want the down and up function both to accept an event parameter (called e in my example).

2. Your down function had a missing closing brace. Not sure if that was a copy/paste error or if that was present in your original code.

3. The rx variable was never declared - maybe also a copy/paste error.

Take a look at the snippet I included below - it might be a helpful reference.

Good luck!

 let rx = 0; const rxValueEl = $("#rx-value"); function down(e) { if (e.keyCode === 39) { rx = 3; } if (e.keyCode === 37) { rx = -3; } // Sets value on page rxValueEl.html(rx); } function up(e) { if (rx < 0 && e.keyCode === 37) { rx = 0; } if (rx > 0 && e.keyCode === 39) { rx = 0; } // Sets value on page rxValueEl.html(rx); } document.addEventListener('keydown', down); document.addEventListener('keyup', up);

 <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script> <p>RX value:</p> <p id="rx-value">0</p> <p>Hit left + right arrows to change rx value</p>