不在JavaScript中声明变量时会发生什么？
是的，可以这样做。具有全局作用域时，可以使用变量而无需声明它。下面的“novar”变量“points”将查看作用域链，不使用wincevar关键字-
<html>
<body>
<script>
var rank = 5;
points = 50;
marks = 300;
//匿名功能
(function() {
points = 100; //overwrites global scope points
var rank = 4; //new rank variable is created in this' function's scope
var marks = 900;
document.write(rank+"\r\n"); //prints 4
document.write(points+"\r\n"); //prints 100
document.write(marks+"\r\n"); //prints 900
})();
document.write('<br/>');
document.write('<br/>');
document.write(rank+"\r\n"); //prints 5
document.write(points+"\r\n"); //prints 100
document.write(marks+"\r\n"); //prints 300
</script>
</body>
</html>