即时通讯使用onkeyup（）来调用javascript函数，该函数会添加一些值，而在使用退格键时，它不会减去该值，而是会添加每个值

Question

im using the below function in onkeyup() event of a textbox to add two values of textbox, while entering every digits of numbers in textbox it adds also while deleting number digits it adds the remaining digits, . i wants to decrement the sum value while deleting digits using backspace.

function round_off(){
var inv=document.getElementById("invoice").value ;
var rnd_off=document.getElementById("round_off").value ;
var invo=parseFloat(inv) + parseFloat(rnd_off);
invoice.value=invo.toFixed(2);
}; 

thanks in advance

Answer 1

I'm not sure what you really need, but I guess you can start with this:

function round_off (e) {
    var inv = +document.getElementById('invoice').value,
        rnd_off = +document.getElementById('round_off').value,
        invo;
    if (e.keyCode === 8) { // 8 = Backspace
        invo = inv - rnd_off;
    } else {
        invo = inv + rnd_off;
    }
    invoice.value = invo.toFixed(2);
    return;
}

Notice also, that you'll need to pass event to the handler:

... onkeyup="round_off(event)" ...