逗号运算符，void运算符

逗号运算符

逗号运算符允许多个表达式排在一起，整个表达式返回最右边表达式的值

<script type="text/javascript">
		var a, b , c , d ;
		a= (b = 5, c = 7, d = 56);
		docurnent . write('a ='+a); 
</script>

输出a=56

void运算符

<script type="text/javascript">
		var a, b , c , d ;
		a= void(b = 5, c = 7, d = 56);
		docurnent . write('a ='+a); 
</script>

输出a=undefined