Variables declared with var are permanent : attempting to delete them with the delete operator causes
an error.
If you attempt to read the value of an undeclared variable, JavaScript generates an error. If you assign a
value to a variable that you have not declared with var , JavaScript implicitly declares that variable for
you. Note, however, that implicitly declared variables are always created as global variables, even if they
are used within the body of a function. To prevent the creation of a global variable (or the use of an
existing global variable) when you meant to create a local variable to use within a single function, you
must always use the var statement within function bodies. It's best to use var for all variables, whether
global or local.
an error.
If you attempt to read the value of an undeclared variable, JavaScript generates an error. If you assign a
value to a variable that you have not declared with var , JavaScript implicitly declares that variable for
you. Note, however, that implicitly declared variables are always created as global variables, even if they
are used within the body of a function. To prevent the creation of a global variable (or the use of an
existing global variable) when you meant to create a local variable to use within a single function, you
must always use the var statement within function bodies. It's best to use var for all variables, whether
global or local.
发表评论
-
Extending Built-in Types
2009-01-08 13:55 725The Function.apply( ) method is ... -
Breakpoints using closures
2009-01-07 13:43 869// // This function implements ... -
Private properties with closures
2009-01-07 13:13 760// // This function adds proper ... -
Constructor Functions
2009-01-07 00:42 760the new operator creates a new ... -
Functions as Methods
2009-01-07 00:39 805When a function is invoked as a ... -
The callee Property
2009-01-07 00:02 664In addition to its array elemen ... -
Variable-Length Argument Lists: The Arguments Obje
2009-01-06 23:06 787The Arguments object has one ve ... -
Function Literals
2009-01-06 21:50 702Although function literals crea ... -
Nested Functions
2009-01-06 21:09 767Nested functions may be defined ... -
Deleting Array Elements
2009-01-05 22:11 567The delete operator sets an arr ... -
Reading and Writing Array Elements
2009-01-05 22:00 763Note that array indexes must be ... -
The valueOf() Method
2009-01-05 18:05 742... -
The toLocaleString() Method
2009-01-05 18:02 851In ECMAScript v3 and JavaScript ... -
The constructor Property
2009-01-05 17:51 789[size=medium]Since constructor ... -
the empty statement
2009-01-05 00:29 786[size=medium]When you intention ... -
with
2009-01-05 00:27 683[size=medium]The with statement ... -
try/catch/finnaly
2009-01-05 00:17 890If control leaves the try bloc ... -
throw
2009-01-04 23:56 692The tHRow statement has the fol ... -
return
2009-01-04 23:52 816If a function executes a return ... -
functions
2009-01-04 23:48 789[size=medium]Technically speaki ...
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