JavaScript arrays are simply a specialized kind of object. Therefore, the for/in loop enumerates array
indexes as well as object properties.
The for/in loop does not specify the order in which the properties of an object are assigned to the
variable. There is no way to tell what the order will be in advance, and the behavior may differ among
implementations or versions of JavaScript. If the body of a for/in loop deletes a property that has not yet
been enumerated, that property will not be enumerated. If the body of the loop defines new properties,
whether or not those properties will be enumerated by the loop is implementation-dependent.
The for/in loop does not actually loop through all possible properties of all objects. In the same way that
some object properties are flagged to be read-only or permanent (nondeletable), certain properties are
flagged to be nonenumerable. These properties are not enumerated by the for/in loop. While all userdefined
properties are enumerated, many built-in properties, including all built-in methods, are not
enumerated.
indexes as well as object properties.
The for/in loop does not specify the order in which the properties of an object are assigned to the
variable. There is no way to tell what the order will be in advance, and the behavior may differ among
implementations or versions of JavaScript. If the body of a for/in loop deletes a property that has not yet
been enumerated, that property will not be enumerated. If the body of the loop defines new properties,
whether or not those properties will be enumerated by the loop is implementation-dependent.
The for/in loop does not actually loop through all possible properties of all objects. In the same way that
some object properties are flagged to be read-only or permanent (nondeletable), certain properties are
flagged to be nonenumerable. These properties are not enumerated by the for/in loop. While all userdefined
properties are enumerated, many built-in properties, including all built-in methods, are not
enumerated.
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Extending Built-in Types
2009-01-08 13:55 732The Function.apply( ) method is ... -
Breakpoints using closures
2009-01-07 13:43 878// // This function implements ... -
Private properties with closures
2009-01-07 13:13 775// // This function adds proper ... -
Constructor Functions
2009-01-07 00:42 783the new operator creates a new ... -
Functions as Methods
2009-01-07 00:39 813When a function is invoked as a ... -
The callee Property
2009-01-07 00:02 671In addition to its array elemen ... -
Variable-Length Argument Lists: The Arguments Obje
2009-01-06 23:06 798The Arguments object has one ve ... -
Function Literals
2009-01-06 21:50 708Although function literals crea ... -
Nested Functions
2009-01-06 21:09 773Nested functions may be defined ... -
Deleting Array Elements
2009-01-05 22:11 580The delete operator sets an arr ... -
Reading and Writing Array Elements
2009-01-05 22:00 783Note that array indexes must be ... -
The valueOf() Method
2009-01-05 18:05 756... -
The toLocaleString() Method
2009-01-05 18:02 866In ECMAScript v3 and JavaScript ... -
The constructor Property
2009-01-05 17:51 797[size=medium]Since constructor ... -
the empty statement
2009-01-05 00:29 796[size=medium]When you intention ... -
with
2009-01-05 00:27 689[size=medium]The with statement ... -
try/catch/finnaly
2009-01-05 00:17 899If control leaves the try bloc ... -
throw
2009-01-04 23:56 700The tHRow statement has the fol ... -
return
2009-01-04 23:52 823If a function executes a return ... -
functions
2009-01-04 23:48 809[size=medium]Technically speaki ...
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