计算器编码 - 添加分数按钮

Question

我有一个示例计算器JavaScript套件，我正在尝试修改它以添加一些分数按钮（将小数转换为分数＆amp;反之亦然，使用数字来制作分数，例如按2然后一个按钮然后按下4并使其成为2/4或1/2，然后对分割符号后面的数字执行相同操作，这样它就像2/4除以1/2。这是计算器代码，带有头部脚本和身体本身。

HEAD

<SCRIPT LANGUAGE="JavaScript" id="calculator">
function addChar(input, character) {
    if(input.value == null || input.value == "0")
        input.value = character
    else
        input.value += character
}

function cos(form) {
    form.display.value = Math.cos(form.display.value);
}

function sin(form) {
    form.display.value = Math.sin(form.display.value);
}

function tan(form) {
    form.display.value = Math.tan(form.display.value);
}

function sqrt(form) {
    form.display.value = Math.sqrt(form.display.value);
}

function ln(form) {
    form.display.value = Math.log(form.display.value);
}

function exp(form) {
    form.display.value = Math.exp(form.display.value);
}

function deleteChar(input) {
    input.value = input.value.substring(0, input.value.length - 1)
}

function changeSign(input) {
    if(input.value.substring(0, 1) == "-")
        input.value = input.value.substring(1, input.value.length)
    else
        input.value = "-" + input.value
}

function compute(form) {
    form.display.value = eval(form.display.value)
}

function square(form) {
    form.display.value = eval(form.display.value) * eval(form.display.value)
}

function checkNum(str) {
    for (var i = 0; i < str.length; i++) {
        var ch = str.substring(i, i+1)
        if (ch < "0" || ch > "9") {
            if (ch != "/" && ch != "*" && ch != "+" && ch != "-" && ch != "."
                && ch != "(" && ch!= ")") {
                alert("invalid entry!")
                return false
                }
            }
        }
        return true
}
</SCRIPT>

BODY

<center><div id="calculator">
    <FORM NAME="sci-calc">
    <TABLE CELLSPACING="0" CELLPADDING="1">
    <TR>
    <TD COLSPAN="5" ALIGN="center"><INPUT NAME="display" VALUE="0" SIZE="28" MAXLENGTH="25"></TD>
    </TR>
    <TR>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE=" exp " ONCLICK="if (checkNum(this.form.display.value)) { exp(this.form) }"></TD>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE="  7  " ONCLICK="addChar(this.form.display, '7')"></TD>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE="  8  " ONCLICK="addChar(this.form.display, '8')"></TD>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE="  9  " ONCLICK="addChar(this.form.display, '9')"></TD>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE="   /   " ONCLICK="addChar(this.form.display, '/')"></TD>
    </TR>
    <TR>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE="  ln   " ONCLICK="if (checkNum(this.form.display.value)) { ln(this.form) }"></TD>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE="  4  " ONCLICK="addChar(this.form.display, '4')"></TD>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE="  5  " ONCLICK="addChar(this.form.display, '5')"></TD>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE="  6  " ONCLICK="addChar(this.form.display, '6')"></TD>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE="   *   " ONCLICK="addChar(this.form.display, '*')"></TD>
    </TR>
    <TR>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE=" sqrt " ONCLICK="if (checkNum(this.form.display.value)) { sqrt(this.form) }"></TD>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE="  1  " ONCLICK="addChar(this.form.display, '1')"></TD>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE="  2  " ONCLICK="addChar(this.form.display, '2')"></TD>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE="  3  " ONCLICK="addChar(this.form.display, '3')"></TD>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE="   -   " ONCLICK="addChar(this.form.display, '-')"></TD>
    </TR>
    <TR>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE="  sq  " ONCLICK="if (checkNum(this.form.display.value)) { square(this.form) }"></TD>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE="  0  " ONCLICK="addChar(this.form.display, '0')"></TD>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE="   .  " ONCLICK="addChar(this.form.display, '.')"></TD>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE=" +/- " ONCLICK="changeSign(this.form.display)"></TD>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE="   +  " ONCLICK="addChar(this.form.display, '+')"></TD>
    </TR>
    <TR>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE="   (    " ONCLICK="addChar(this.form.display, '(')"></TD>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE="cos" ONCLICK="if (checkNum(this.form.display.value)) { cos(this.form) }"></TD>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE=" sin" ONCLICK="if (checkNum(this.form.display.value)) { sin(this.form) }"></TD>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE=" tan" ONCLICK="if (checkNum(this.form.display.value)) { tan(this.form) }"></TD>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE="   )   " ONCLICK="addChar(this.form.display, ')')"></TD>
    </TR>
    <TR>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE="clear" ONCLICK="this.form.display.value = 0 "></TD>
    <TD ALIGN="center" COLSPAN="3"><INPUT TYPE="button" VALUE="backspace" ONCLICK="deleteChar(this.form.display)"></TD>
    <TD ALIGN="center"><INPUT TYPE="button" VALUE="enter" NAME="enter" ONCLICK="if (checkNum(this.form.display.value)) { compute(this.form) }"></TD>
    </TR>
    </TABLE>
    </FORM>
    </div>