格式化字符串：金额

input 输入框输入的数字转换成金额格式：

/*
 * caculate
 * input:  100000
 * output: 100,000
*/
(function ($) {

    var $input = $("#cacu-input"),
        $btn = $("#cacu-btn"),
        $result = $("#cacu-result"),
        result = 0,
        // 只允许数字及后退
        filterNum = function (e) {
            // 数字和后退键以外禁用
            if ((e.keyCode < 48 || e.keyCode > 57) && e.keyCode !== 8) {
                e.preventDefault();
                return false;
            }
        },
        // 格式化金额
        formatCurrency = function (num) {
            num = num.toString().replace(/\$|\,/g, ‘‘);

            if (isNaN(num)) {
                num = "0";
            }

            var sign, cents;  // 正负  小数

            sign = ((Number(num) >= 0) ? ‘‘ : ‘-‘);  //   正负
            num = Math.abs(num*100 + 0.50000000001);
            cents = num%100;

            num = Math.floor(num/100).toString();
            if (cents < 10) {
                cents = ‘0‘ + cents;
            }

            for (var i = 0; i < Math.floor((num.length-(1+i))/3); i++) {
                num = num.substring(0,num.length-(4*i+3))+‘,‘+
                num.substring(num.length-(4*i+3));
            }

            return (sign + num);  // + ‘.‘ + cents;
        },
        getCurrency = function (num) {
            return num.replace(/\$|\,/g, ‘‘);
        };

    $input.on("keypress", function (e) {
        filterNum(e);
    }).on("keyup", function (e) {
        var val = $(this).val();
        val = formatCurrency(val);

        $(this).val(val);
    });

    $btn.on("click", function (e) {
        e.preventDefault();
        var money = $input.val();
        money = getCurrency(money);

        result = parseInt(money/500, 10);
        $result.text(result);
    });
})(window.jQuery);