为什么javascript功能不起作用？

Question

I was using this function to enter only digits in to textbox and it worked.

function isNumberKey(evt) {
    var charCode = (evt.which) ? evt.which : event.keyCode
    if (charCode > 31 && (charCode < 48 || charCode > 57))
        return false;

    return true;
}

but customer asked me to restrict - sign so user should not enter - sign. So i modified the code to this

function isNumberKey(evt) {
    var charCode = (evt.which) ? evt.which : event.keyCode
    if (charCode > 31 && (charCode < 48 || charCode > 57) && charCode == 45)
        return false;

    return true;
}

and now it not works, it allows letters too, why ?

Answer 1

You need || in the group:

 function isNumberKey(evt) { var charCode = (evt.which) ? evt.which : event.keyCode; var bool = (charCode > 31) && (charCode < 48 || charCode > 57 || String.fromCharCode(charCode) == "-"); return !bool; } 

 <input type="text" onkeypress='return isNumberKey(event)'> 

Answer 2

You should use || instead of && in your test.
On my azerty keyboard, the - sign charcode is 54 , not 45 .

function isNumberKey(evt) {
    var charCode = (evt.which) ? evt.which : event.keyCode
    if (charCode > 31 && (charCode < 48 || charCode > 57 || charCode == 45) )
        return false;

    return true;
}

See this fiddle

Edit

Looks like your charCode is correct . The 54 value comes from my azerty keyboard.
Nevertheless, you should use || instead of && in your check.