表达式的校验

校验一个运算表达式的格式是否正确


 1 var validateExp = function(str){
 2   // str为字符串表达式，里面的内容只能包括运算符(+、-、*、/)，还有左右括号，剩下的变量值可以用a-z来表示，如表达式：a+b、(a+b)*c等
 3   let operaList = ["+","-","*","/"]; // 运算符
 4   let LandOperaList = ["("].concat(operaList);
 5   let RandOperaList = [")"].concat(operaList)
 6   let validateFlag = true; //
 7   let errorTip = ""; //错误信息
 8   let strArr = (str||"").trim().replace(/s/g,"").split("");//整理字符串表达式为数组
 9   if(!strArr.length){
10     return "表达式字符串不可为空"
11   }
12   var leftCount = strArr.filter(one=>{return one=="("}).length;
13   var rightCount = strArr.filter(one=>{return one==")"}).length;
14   if(leftCount!=rightCount){
15     return "左右括号不成对"
16   } 
17   for(var i=0;i<strArr.length;i++){
18     var value = strArr[i];
19     var beforeValue = strArr[i-1];
20     var afterValue = strArr[i+1];
21     if(value == "("){
22       if(beforeValue&&LandOperaList.indexOf(beforeValue)<0){
23         validateFlag = false;
24         errorTip = "第"+Number(i+1)+"个字符："+value+" 前面不正确"
25       }else if(RandOperaList.indexOf(afterValue)>-1){
26         validateFlag = false;
27         errorTip = "第"+Number(i+1)+"个字符："+value+" 后面不正确"
28       };
29     }else if(value == ")"){
30       if(LandOperaList.indexOf(beforeValue)>-1){
31         validateFlag = false;
32         errorTip = "第"+Number(i+1)+"个字符："+value+" 前面不正确"
33       }else if(afterValue&&RandOperaList.indexOf(afterValue)<0){
34         validateFlag = false;
35         errorTip = "第"+Number(i+1)+"个字符："+value+" 后面不正确"
36       };
37     }else if(operaList.indexOf(value)>-1){
38       if(LandOperaList.indexOf(beforeValue)>-1){
39         validateFlag = false;
40         errorTip = "第"+Number(i+1)+"个字符："+value+" 前面不正确"
41       } else if(RandOperaList.indexOf(afterValue)>-1){
42         validateFlag = false;
43         errorTip = "第"+Number(i+1)+"个字符："+value+" 后面不正确"
44       }
45     } else {
46       if(beforeValue&&LandOperaList.indexOf(beforeValue)<-1){
47         validateFlag = false;
48         errorTip = "第"+Number(i+1)+"个字符："+value+" 前面不正确"
49       } else if(afterValue&&RandOperaList.indexOf(afterValue)<-1){
50         validateFlag = false;
51         errorTip = "第"+Number(i+1)+"个字符："+value+" 后面不正确"
52       }
53     }
54         
55     if(!validateFlag){
56       break;
57     }
58   }
59   if(!validateFlag){
60     return errorTip
61   } else {
62     return "表达式正确"
63   }
64 }