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// 改变引用
// Set items to an array (object) of strings
var items = new Array( “one”, “two”, “three” );
// Set itemsRef to a reference to items
var itemsRef = items;
// Set items to equal a new object
items = new Array( “new”, “array” );
// items and itemsRef now point to different objects.
// items points to new Array( “new”, “array” )
// itemsRef points to new Array( “one”, “two”, “three” )
alert( items !== itemsRef );

// String是值传递
// Set item equal to a new string object
var item = “test”;
// itemRef now refers to the same string object
var itemRef = item;
// Concatenate some new text onto the string object
// NOTE: This creates a new object, and does not modify
// the original object.
item += “ing”;
// The values of item and itemRef are NOT equal, as a whole
// new string object has been created
alert( item != itemRef );

方法重载和类型检查
// 通过判断arguments的长度来重载
// A simple function for sending a message
function sendMessage( msg, obj ) {
// If both a message and an object are provided
if ( arguments.length == 2 )
// Send the message to the object
obj.handleMsg( msg );
// Otherwise, assume that only a message was provided
else
// So just display the default error message
alert( msg );
}

// 任意长参数，直接操作arguments，就实现了java的不定长参数了
// A function that takes any number of arguments and makes
// an array out of them
function makeArray() {
// The temporary array
var arr = [];
// Go through each of the submitted arguments
for ( var i = 0; i < arguments.length; i++ ) {
arr.push( arguments[i] );
}
// Return the resulting array
return arr;
}

//typeof操作符
function displayError( msg ) {
// Check and make sure that msg is not undefined
if ( typeof msg == ‘undefined’ ) {
// If it is, set a default message
msg = “An error occurred.”;
}
// Display the message
alert( msg );
}

// 用typeof确定对象类型
// Check to see if our number is actually a string
if ( typeof num == “string” )
// If it is, then parse a number out of it
num = parseInt( num );
// Check to see if our array is actually a string
if ( typeof arr == “string” )
// If that’s the case, make an array, splitting on commas
arr = arr.split(“,”);

//用constructor确定对象类型
// Check to see if our number is actually a string
if ( num.constructor == String )
// If it is, then parse a number out of it
num = parseInt( num );
// Check to see if our string is actually an array
if ( str.constructor == Array )
// If that’s the case, make a string by joining the array using commas
str = str.join(‘,’);

// 用constructor来做类型限定
// Strictly check a list of variable types against a list of arguments
function strict( types, args ) {
// Make sure that the number of types and args matches
if ( types.length != args.length ) {
// If they do not, throw a useful exception
throw “Invalid number of arguments. Expected ” + types.length +
“, received ” + args.length + ” instead.”;
}
// Go through each of the arguments and check their types
for ( var i = 0; i < args.length; i++ ) {
//
if ( args[i].constructor != types[i] ) {
throw “Invalid argument type. Expected ” + types[i].name +
“, received ” + args[i].constructor.name + ” instead.”;
}
}
}
// A simple function for printing out a list of users
function userList( prefix, num, users ) {
// Make sure that the prefix is a string, num is a number,
// and users is an array
strict( [ String, Number, Array ], arguments );
// Iterate up to ‘num’ users
for ( var i = 0; i < num; i++ ) {
// Displaying a message about each user
print( prefix + “: ” + users[i] );
}
}

// 变量作用域
最外面都是window的变量，全局变量
函数里面可以直接访问全局变量，varname,window.varname
函数里面var声明的变量是局部变量

//一个函数返回一个新的函数
// A function that generates a new function for adding numbers
function addGenerator( num ) {
// Return a simple function for adding two numbers
// with the first number borrowed from the generator
return function( toAdd ) {
return num + toAdd
};
}
// addFive now contains a function that takes one argument,
// adds five to it, and returns the resulting number
var addFive = addGenerator( 5 );
// We can see here that the result of the addFive function is 9,
// when passed an argument of 4
alert( addFive( 4 ) == 9 );

//匿名函数使内部变量隐藏起来，不和外部变量冲突
(function(){
// The variable that would, normally, be global
var msg = “Thanks for visiting!”;
// Binding a new function to a global object
window.onunload = function(){
// Which uses the ‘hidden’ variable
alert( msg );
};
// Close off the anonymous function and execute it
})();

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