Writing Scripts in Nashorn - Scripting in Java: Integrating with Groovy and JavaScript - page 95

Accessing Object's Properties
You can access properties of an object using property accessor expressions using one of
the two syntax:

• Using the Dot Notation

• Using the Bracket Notation

The dot notation uses the following syntax:

objectExpression.property

The objectExpression is an expression that evaluates to the reference to the object
and the property is the property name.
The bracket notation uses an array-like syntax:

objectExpression[propertyExpression]

The objectExpression is an expression that evaluates to the reference to the object.
It is followed with an opening bracket and a closing bracket. The propertyExpression is
an expression that is convertible to a string and that is the property name being accessed.

■ if the property name contains whitespaces or stored in a variable, you must use the
bracket notation, not the dot notation, to access the property.

Tip

Consider the following object from the previous section:

// An object with whitespaces in the property names
var redColor = {"red value": 1.0,
green: 0.0,
"black Value": 0.0,
alpha: 1.0};

The following statement reads the value of the alpha property of the object into a
variable named alphaValue :

// Assigns 1.0 to alphaValue
var alphaValue = redColor.alpha;

If the property accessor expression appears on the right side of the assignment
operator, you are setting a new value for the property. The following statement sets the
alpha property of the redColor object to 0.5:

// Make the color semi-transparent
redColor.alpha = 0.5;