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5.11. Other Operators

The remaining operators apply to topics considered in other chapters. We'll include them here for quick reference only and describe their usage fully in those chapters.

5.11.5. Array-Element/Object-Property Operator

As we'll see in Chapter 11, "Arrays" and Chapter 12, "Objects and Classes", we use the [ ] operator to retrieve and set the value of an array element or an object property. When accessing an array it takes the form:

array[element]

where array is the name of an array or an array literal and element is an expression that resolves to a zero-relative, non-negative integer representing the index of the array element to access.

When accessing an object, it takes the form:

object[property]

where object is an object name or object literal and property is any expression that resolves to a string representing the name of the object property to access.

When used on the left side of an assignment operator (=), the element or property is assigned the new value shown on the right side of the expression:

var colors = new Array( );  // Create a new array
colors[0] = "orange";      // Set its first element
colors[1] = "green";       // Set its second element

var ball = new Object( );   // Create a new object
var myProp = "xVelocity";  // Store a string in a variable
ball["radius"] = 150;      // Set the radius property
ball[myProp] = 10;         // Set the xVelocity property through myProp

When used anywhere else, the expression returns the value of the specified element or property:

diameter = ball["radius"] * 2;  // Sets diameter to 300
trace(colors[0]);               // Displays "orange"


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