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Summary

return iNum1 + iNum2 + iBaseNum;

}

return doAddition();

}

Here, the function

addNumbers()

contains a function (the closure) named

doAddition()

. The internal

function is a closure because it captures the arguments of the outer function,

iNum1

and

iNum2

, as well

as the global variable

iBaseNum

. The last step of

addNumbers()

calls the inner function, which adds the

two arguments and the global variable and returns the value. The important concept to grasp here is that

doAddition()

doesn’t accept any arguments at all; the values it uses are captured from the execution

environment.

As you can see, closures are a very powerful, versatile part of ECMAScript that can be used to perform

complex calculations. Just as when you use any advanced functionality, exercise caution when using clo-

sures because they can get extremely complex.

Summary

This chapter looked at the basics of ECMAScript:

General syntax

Defining variables using the

var

keyword

Primitive and reference values

The basic primitive types (Undefined, Null, Boolean, Number, and String)

The basic reference types (Object, Boolean, Number, and String)

Operators and statements

Functions

Understanding ECMAScript is an important part of JavaScript programming, which is why this chapter

is perhaps the most important in this book. A good grasp of the core is vital to comprehending the rest of

the topics in the book.

The next chapter focuses on more of the object-oriented aspects of ECMAScript, including how to create

your own classes and how to establish inheritance.

Chapter 2

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