/*

Append the names of the enumerable properties of object o to the array a, and return a.

If a is omitted or null, create and return a new array

*/

function

copyPropertyNamesToArray(o,

/*

optional

*/

a) {

if

(

!

a) a

=

[];

//

/If undefined or null , use a blank array

for

(

var

perperty

in

o) a.push(perperty)

return

;

}

/*

arguments 类似 Math.max()

*/

function

max(

/*

.....

*/

) {

var

m

=

Number.NEGATIVE_INFINITY;

//

//Loop through all the arguments , looking for, and

//

// remembering, the biggest

for

(

var

i

=

0

; i

<

arguments.length; i

++

)

if

(arguments[i]

>

m) m

=

arguments[i];

return

m;

}

/*

判断传递给函数的参数个数是否符合要求

*/

function

check(args) {

var

actual

=

args.length;

var

expected

=

args.callee.length;

if

(actual

!=

expected) {

throw

new

Error(

"

Wrong number of arguments: expected:

"

+

expected

+

"

; actually passed

"

+

actual);

}

}

function

f(x, y, z) {

check(arguments);

return

x

+

y

+

z;

}

/*

程序员偶尔会想要编写一个通过调用来记住一个值的函数。这个值不能存储在一个局部变量中，因为调用对象不能通过调用来维持。尽量不用全局变量

*/

uniqueId

=

function

() {

if

(

!

arguments.callee.id) arguments.callee.id

=

0

;

return

arguments.callee.id

++

;

}

CuniqueId

=

(

function

() {

//

The call object of this function holds our value

var

id

=

0

;

//

this is the private persistent value

//

The outer function returns a nested function that has access

//

to the persistent value. It is the nested function we're storing

//

in the variable uniqueId above

return

function

() {

return

id

++

};

//

Return and increment

})();

//

Invoke the outer function after defining it.