HTML and CSS Reference
F or...in loops through the properties and methods of an object. The
variable prop is set to the label associated with the property or method.
You'll see it used most often in scripts that check to see if a browser
supports certain HTML5 features. Note that the syntax myObject
['myProperty'] is an alternative way of accessing the myProperty method.
This alternative approach is handy for use inside for...in loops.
Before we finish with objects, it's important to know that variables that
refer to objects behave slightly differently than variables that refer to
normal values like numbers. To see the difference, let's do a little
experiment in the console.
1 Create a variable a , and give it the
value 2 .
2 Create a variable b , and give it the
value of a .
3 Set the variable b to have a value of
Notice that after you do this, the value
of a is unchanged. Setting b to have a
value of a doesn't create any sort of
relationship between them. The value
contained in a is copied into b .
Now try a similar sequence of opera-
tions with two variables that refer to
objects. Notice that after assigning
myObject as the value of myOtherObject ,
changing the value of myOtherObject
.myProperty also changes the value of
myObject.myProperty . This is because
assigning the object to another vari-
able creates two variables that refer to
the same object .