テキストボックスに数字のみを入力させる

KeyDownに紐付ける

function number_check(e){
    // left, right, enter, backspace or numbers
    if( e.which != 37 && e.which != 39 && e.which != 13 && e.which!=8 && 
        e.which!=0 && (e.which<48 || e.which>57) && (e.which<95 || e.which>106)) return false;
        return true;
}

参考URL:
http://www.cambiaresearch.com/articles/15/javascript-char-codes-key-codes