How do you circumvent repeated keydown messages when you want to use them with javascript where you hold the key down but want it only to play once?

问题

I have a piece of code that looks something like below and it works fine. What it does is it launches an oscillator sound when the mouse clicks on a div named synth.It then stops playing the oscillator when the mouse button is released.

 synth.onmousedown= function () {
    oscillator = context.createOscillator(),  // Creates the oscillator 
    oscillator.type = synthWaveform.value;  
    oscillator.frequency.value = pitchInput.value;                   
    oscillator.connect(context.destination);  // Connects it to output
    oscillator.noteOn(0); 


    };



    synth.onmouseup = function ()    {  
    oscillator.disconnect(); 

    };

I then added the code below so that when a user presses a keyboard charachter it triggers the oscillator. The problem is that when the key is held down it repeadedly plays and then won't stop when the keyboard character is released. I want to know if there are any libraries or code that can be used to circumvent this. The goal is to have the end result be like a mousedown/up effect but with keyboard movements triggering the sound.Thank you.

$('body').keydown(function() {
oscillator = context.createOscillator(),  // Creates the oscillator 
oscillator.type = synthWaveform.value;  
oscillator.frequency.value = pitchInput.value;                   
oscillator.connect(context.destination);  // Connects it to output
oscillator.noteOn(0); 
});

$('body').keyup(function() {
oscillator.disconnect();

});

回答1:

you could use underscore.js debounce if you need something fancier than the below option.

var keydown = false;

$('body').keydown(function() {
    if(!keydown){
        oscillator = context.createOscillator(),  // Creates the oscillator 
        oscillator.type = synthWaveform.value;  
        oscillator.frequency.value = pitchInput.value;                   
        oscillator.connect(context.destination);  // Connects it to output
        oscillator.noteOn(0);
        keydown = true;
    }
});

$('body').keyup(function() {
    oscillator.disconnect();
    keydown = false;
});

回答2:

This might be a workaround

var keyIsDown = false;

$('body').keydown(function() {
    if(keyIsDown) {
       // key is already down
       return true;
    }

    keyIsDown = true;

    // do your keydown handler
}

$('body').keyup(function() {
    keyIsDown = false;
}

来源：https://stackoverflow.com/questions/14301728/how-do-you-circumvent-repeated-keydown-messages-when-you-want-to-use-them-with-j

标签

javascript

dom

keypress