js表达式计算器代码_javascript技巧

效果图：

代码:

<script type="text/javascript">// <![CDATA[ String.prototype.trim = function () { return this.replace(/^\s+/, '').replace(/\s+$/, ''); }; function calc() { var expression = document.getElementById("txtExpression").value; try { document.getElementById("txtResult").innerText ='计算结果为:'+ calcBasic(calcComplex(expression)); } catch(e) { document.getElementById("txtResult").innerText = e.message; } } function calcComplex(complexExpression) { var arr = new Array(); var left = 0; var right = 0; for (var i = 0; i < complexExpression.length; i++) { if (complexExpression.charAt(i) == '(') { arr.push(i); left++; } if (complexExpression.charAt(i) == ')') { arr.push(i); right++; } } if (left != right) { throw new Error('括号不匹配！','2'); } var brackets = complexExpression.replace(/[^\(|^\)]/g, ''); for (i = 0; i < brackets.length; i++) { if (brackets.charAt(i) == "(" && brackets.charAt(i + 1) == ")") { var simpleExpression = complexExpression.substr(arr[i] + 1, arr[i + 1] - arr[i] - 1); if (calcBasic(simpleExpression)<0) { complexExpression = complexExpression.substr(0, arr[i]) + '[' + Math.abs(calcBasic(simpleExpression)) + '' + complexExpression.substr(arr[i + 1] + 1); } else { complexExpression = complexExpression.substr(0, arr[i]) + '' + calcBasic(simpleExpression) + '' + complexExpression.substr(arr[i + 1] + 1); } complexExpression=calcComplex(complexExpression); break; } } return complexExpression; } function calcBasic(baseExpression) { if (baseExpression.charAt(0)=='-') { baseExpression = '[' + baseExpression.substr(1); } var constants = baseExpression.trim().replace(/[\*|\/|\+|\-]/g, ' ').split(/\s+/g); for (var index in constants) { //只留下符号 baseExpression = baseExpression.replace(/\s+/g, '').replace(constants[index], ''); //将提取的常量字符串转化为数字 var item; if (constants[index].trim().charAt(0)=='[') { item = parseFloat(constants[index].trim().replace('[','-')); } else { item = parseFloat(constants[index].trim()); } if (isNaN(item)) { throw new Error('存在非法符号！','0'); } else { constants[index] = item; } } if (constants.length != baseExpression.length + 1) { throw new Error('表达式有误！','1'); } for (var i = 0; i < baseExpression.length; i++) { switch (baseExpression.charAt(i)) { case '*': constants.splice(i, 2, constants[i] * constants[i + 1]); baseExpression = baseExpression.replace('*', ''); i -= 1; break; case '/': if (constants[i + 1] == 0) { throw new Error('除数不能为0！'); } constants.splice(i, 2, constants[i] / constants[i + 1]); baseExpression = baseExpression.replace('/', ''); i -= 1; break; default: break; } } for (var j = 0; j < baseExpression.length; j++) { switch (baseExpression.charAt(j)) { case '+': constants.splice(j, 2, constants[j] + constants[j + 1]); baseExpression = baseExpression.replace('+', ''); j -= 1; break; case '-': constants.splice(j, 2, constants[j] - constants[j + 1]); baseExpression = baseExpression.replace('-', ''); j -= 1; break; default: break; } } return constants[0]; } // ]]></script> <div style="text-align: center;"> <textarea id="txtExpression" style="width: 90%; height: 200px; overflow-y: visible;"> <div style="width: 90%; margin: 4px auto; text-align: left;"> <input id="btnSubit" type="button" onclick="calc()" value="计算"> <span id="txtResult"></span> </div>
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