Please look at the following code:

<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
</head>
<body>
    <script>
        var a=10,b=20,c=30;
        ++a;
        a++;
        e=++a+(++b)+(c++)+a++;
        alert(e);
    </script>
</body>
</html>

To answer this question, first understand: i What is returned is The value before auto-increment, i returns the value after auto-increment.

如：
var i = 1;
var a = i++;  //a = 1;  此时i先将值1赋给a,然后自己+1，i=2;
var b = ++i;  //b = 3；此时i先自己+1为3.再给b赋值，b=3;

再看此题：那么++a意思为a=a+1 a为11，此时不涉及运算优先级的问题。

		a++意思为a=a+1       a为12  ，此时仍旧不涉及运算优先级的问题。

		当e=++a+(++b)+(c++)+a++;时，必须考虑运算级的问题。

		此时：++a a先自己+1  然后将值赋给结果：13      a=13

			++b  b先自己+1  然后将值赋给结果：21      b=21

			C++ 先将c值赋给结果：30     c自己+1      c=31

			a++ 先将a值13赋给结果:13   a自己+1       a=14
			此时所有结果加起来：13+21+30+13=77
			本文讲解了JS中运算符i++与++i的详细分析，更多相关内容请关注php中文网。
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