Java Reference
In-Depth Information
It takes an object called
options
as an argument. If no object is provided, we create an
empty object instead in this line:
options = options || {};
This is a common JavaScript pattern used to create default values. It relies on the logical
OR statement being lazily evaluated. If
options
already exists, only the first statement
will be evaluated, so
options
will remain as its current value. If no arguments are sup-
plied to the function, the value of
options
will be
undefined
, which is falsy. Then the
second operand will be evaluated and
options
will be assigned to an empty object literal.
The same method is then used to set default values for the
greeting
,
name
, and
age
properties of the
options
object. At the end of the method, a string is returned that uses
the values that were supplied, or the default values.
Here is an example of how the function can be used:
greet({ greeting: "Hi", age: 10, name: "Bart" });
<< "Hi! My name is Bart and I am 10 years old."
You can enter the parameters in any order and if you don't enter one of the values, its de-
fault value will be used:
greet({ name: "Lisa", age: 8 });
<< "Hello! My name is Lisa and I am 8 years old."
This is a popular pattern used with functions, particularly when there are a lot of options,
and it is common to many JavaScript libraries.
Warning: Be Careful with Falsy Values
You have to take care when using this method of assigning default values
because any falsy value will result in the default value being used.
For example, if an age of
0
is entered, the default value will be used because
0
is falsy:
