理解Javascript_14_函数形式参数与arguments

function say(msg,other,garbage){
alert(arguments[1]);//world
var other = 'nice to meet you!';
var msg;
alert(arguments.length);
alert(msg);//hello
alert(other);//nice to meet you!
alert(arguments[1]);//nice to meet you!
alert(garbage);//undefined
}
say('hello','world');

function say(msg,other,garbage){
//先对函数声明的变量进行'预解析',内部执行流程，它是是不可见的
var msg = undefined;
var other = undefined;
var garbage = undefined;
//再对函数内部定义的变量进行'预解析'
var other = undefined;//很明显，此时这个定义已经无意义了。
var msg = undefined;//无意义
//对实际参数进行赋值操作
msg = new String('hello');//arguments的会将所有实际参数当作对象看待
other = new String('world');
//正式进入函数代码部分
alert(arguments[1]);//world
other = 'nice to meet you!';
//var msg;这个已经被预解析了，因此不会再执行
alert(arguments.length);//2
alert(msg);//hello
alert(other);//nice to meet you!
alert(arguments[1]);//nice to meet you!
alert(garbage);//undefined
}