如何在不使用 eval 的情况下使用 JavaScript 的功能来创建计算器？
[英]How can I use JavaScript's functionality to create a calculator without using eval?
问题描述
It's a little mess, but I need JavaScript's function to calculate.
有点乱，但我需要JavaScript的函数来计算。 I avoided using eval because my teacher has not taught that.我避免使用eval因为我的老师没有教过这个。 Can help me with it?可以帮我吗？
function A7() { var num = document.getElementById(7).value; document.getElementById("display").value = document.getElementById("display").value + num } function A8() { var num = document.getElementById(8).value; document.getElementById("display").value = document.getElementById("display").value + num } function A9() { var num = document.getElementById(9).value; document.getElementById("display").value = document.getElementById("display").value + num } function A10() { var num = document.getElementById(10).value; document.getElementById("display").value = document.getElementById("display").value + num } function A4() { var num = document.getElementById(4).value; document.getElementById("display").value = document.getElementById("display").value + num } function A5() { var num = document.getElementById(5).value; document.getElementById("display").value = document.getElementById("display").value + num } function A6() { var num = document.getElementById(6).value; document.getElementById("display").value = document.getElementById("display").value + num } function A11() { var num = document.getElementById(11).value; document.getElementById("display").value = document.getElementById("display").value + num } function A1() { var num = document.getElementById(1).value; document.getElementById("display").value = document.getElementById("display").value + num } function A2() { var num = document.getElementById(2).value; document.getElementById("display").value = document.getElementById("display").value + num } function A3() { var num = document.getElementById(3).value; document.getElementById("display").value = document.getElementById("display").value + num } function A12() { var num = document.getElementById(12).value; document.getElementById("display").value = document.getElementById("display").value + num } function A0() { var num = document.getElementById(0).value; document.getElementById("display").value = document.getElementById("display").value + num } var firstNum = getElementById(display); document.getElementById("display").value = document.getElementById("display").value + num var secondNum = getElementById(display); document.getElementById("display").value = document.getElementById("display").value + num operation = ""; function calculate() { if (operation = "+") { firstNum + secondNum; document.getElementById("display").value = firstNum + secondNum; } else if (operation = "-") { firstNum - secondNum; document.getElementById("display").value = firstNum - secondNum; } else if (operation = "/") { firstNum / secondNum; document.getElementById("display").value = firstNum / secondNum; else { firstNum * secondNum; document.getElementById("display").value = firstNum * secondNum; } }
<BODY> <form> <TABLE> <TR> <TD COLSPAN="4"> <INPUT TYPE="text" ID="display" style="text-align:right"> </TD> </TR> <TR> <TD> <INPUT TYPE="BUTTON" VALUE="7" ID="7" onclick="A7()"> </TD> <TD> <INPUT TYPE="BUTTON" VALUE="8" ID="8" onclick="A8()"> </TD> <TD> <INPUT TYPE="BUTTON" VALUE="9" ID="9" onclick="A9()"> </TD> <TD> <INPUT TYPE="BUTTON" VALUE="/" ID="10" onclick="A10()"> </TD> </TR> <TR> <TD> <INPUT TYPE="BUTTON" VALUE="4" ID="4" onclick="A4()"> </TD> <TD> <INPUT TYPE="BUTTON" VALUE="5" ID="5" onclick="A5()"> </TD> <TD> <INPUT TYPE="BUTTON" VALUE="6" ID="6" onclick="A6()"> </TD> <TD> <INPUT TYPE="BUTTON" VALUE="*" ID="11" onclick="A11()"> </TD> </TR> <TD> <INPUT TYPE="BUTTON" VALUE="1" ID="1" onclick="A1()"> </TD> <TD> <INPUT TYPE="BUTTON" VALUE="2" ID="2" onclick="A2()"> </TD> <TD> <INPUT TYPE="BUTTON" VALUE="3" ID="3" onclick="A3()"> </TD> <TD> <INPUT TYPE="BUTTON" VALUE="-" ID="12" onclick="A12()"> </TD> <TR> <TD> <INPUT TYPE="BUTTON" VALUE="0" ID="0" onclick="A0()"> </TD> <TD> <INPUT TYPE="reset" VALUE="C" ID="C"> </TD> <TD> <INPUT TYPE="BUTTON" VALUE="=" ID="14" onclick="calculate()"> </TD> <TD> <INPUT TYPE="BUTTON" VALUE="+" ID="13" onclick="A13()"> </TD> </TR> </BODY>
1 个解决方案
解决方案1
2 2018-11-06 01:38:41
calculate() needs to parse the display field to get the two numbers and the operation. calculate()需要解析display字段以获取两个数字和操作。 You can do this with a simple regular expression.你可以用一个简单的正则表达式来做到这一点。
Also, you need to use == to compare strings, not = , which is for assigning.此外，您需要使用==来比较字符串，而不是用于分配的= 。
There's no point in writing line like像这样写行没有意义
firstNum + secondNum;
This calculates the sum but doesn't do anything with it.这会计算总和，但对它没有任何作用。 You only need the lines that assign the result of the calculation to the display value.您只需要将计算结果分配给display值的行。
function calculate() { var input = document.getElementById("display").value.match(/^(\\d+)([+\\-*\\/])(\\d+)$/); if (!input) { alert("Nothing to calculate"); return; } var firstNum = parseInt(input[1]); var operation = input[2]; var secondNum = parseInt(input[3]); if (operation == "+") { document.getElementById("display").value = firstNum + secondNum; } else if (operation == "-") { document.getElementById("display").value = firstNum - secondNum; } else if (operation == "/") { document.getElementById("display").value = firstNum / secondNum; } else { document.getElementById("display").value = firstNum * secondNum; } }
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