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 }
