自动删除新字符 javascript

Question

我正在为学校做一个实验室，目标是创建一个 Web 控件，只接受来自用户的货币值。

Rules:
1st digit must be “-“ or “$”
2nd digit must be “$” or a number
3rd digit on must be a number or a “.”
Only two digits after decimal
Must have a “$”

我遇到的问题是，虽然我可以设置标签以在允许或不允许某些内容时显示，但我无法弄清楚如何让它在条件不允许时自动删除新字符'没遇到过。（例如，不能输入“-1”，只能输入“-$”或“$1”。）尝试设置子字符串的长度似乎不起作用。当前示例中的条件似乎也仅在字符串仅由“-”组成时才有效。添加的任何额外字符都不会触发它。

代码：

    function text2money(e) {
        // get value of txt
        var str = document.getElementById("<%=txt.ClientID %>").value;

        if (str.substring(0, str.length) === "-" && str.substring(1, str.length) !== "$") {
                str.length = 2;
        }

        // goes through string one character at a time, converts them to char, then checks if char is a decimal digit
        if (str.substring(0, 1) === ('-') || str.substring(0, 1) === ('$')) {
            document.getElementById("<%= lbl1.ClientID %>").innerHTML = "True"; // must use .innerHTML with labels

            // check if second digit is '$' or numeric
            if (str.substring(1, 2) === ("$") || isFinite(str.substring(1, 2))) {
                document.getElementById("<%= lbl1.ClientID %>").innerHTML = "It's numeric";

                // check if third and any future characters are '.' or numeric

            } // end second char if

            else {
                document.getElementById("<%= lbl1.ClientID %>").innerHTML = "Second char must be '$' or numeric";
            } // end second char

        } // end first char if
        else {
            document.getElementById("<%= lbl1.ClientID %>").innerHTML = "First character must be '-' or '$'";
        } // end first char

        // check if $ is included anywhere in the string
        var result = str.indexOf("$") <= -1; // -1 == false
        if (result) {
            document.getElementById("<%= lbl2.ClientID %>").innerHTML = "$ is a required character";
            }
            else {
                document.getElementById("<%= lbl2.ClientID %>").innerHTML = "";
            }

        } // end text2money

Answer 1

使用 Regex 对象：

        (/^-?$\d+\.\d{2}$/).test(inputString)

/^ 将模式的开始定义为字符串的开始

-? 1 个可选 -

\$ 1 必填 $

\d+ 1个或多个数字

。强制性的。

\d{2} 恰好 2 位数

$/ 字符串的强制结尾

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