js表达式计算器代码,js计算器效果演示

<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>
</p>
<div style="text-align: center;"><textarea id="txtExpression" style="width: 90%; height: 200px; overflow-y: visible;"></textarea>
<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>