JavaScript: The First Parts Part One Douglas Crockford Yahoo! Inc

JavaScript: The First Parts

Part One

Douglas Crockford

Yahoo! Inc.

Learn to Program

• Values

• Variables

• Expressions

• Branching

• Loops

• Functions

• Recursion

• Arrays

• Objects

• Trees

Why should you learn to program?

In programming we construct and maintain extremely complex systems with

aspirations of perfection.

Ulterior Motives

Programming Languages

JavaScript

The world's most misunderstood programming

language.

Learn to Program

• Values

• Variables

• Expressions

• Branching

• Loops

• Functions

• Recursion

• Arrays

• Objects

• Trees

Values

Numbers, strings, booleans

null

undefined

Variables

Values stored under names.

The values can be replaced.

Expressions

Elements of computation

Branching

Alter the sequential flow of the program

Loops

Repetitive operations

Functions

Encapsulated expressions

Recursion

Functions defined in terms of themselves

Arrays

Linear sequences of storage

Objects

Associative collections of named values

Trees

Complex structures composed of objects

Inside every programming language there is a calculator

• Literal numbers with infix operators

• * used for multiplication

• / is used for division

• Precedence

• ( ) can change precedence

2 + 3 * 4 === 14

(2 + 3) * 4 === 20

The Yellow Box

http://jsmvhs.crockford.com/yellowbox.html

Try these

0.3 - 0.1

0.3 - 0.1 - 0.1 - 0.1

1 / 0

• JavaScript numbers don't always work like real numbers.

The result of an expression can be stored

in a variablea = 3 + 4

a = a + 1

The naming of variables is a serious matter

• It isn't just one of your holiday games.

• Well chosen names can make a program self descriptive.

• A variable name should begin with a letter.

• It can contain any number of letters and digits.

• It can contain the _ (underline) character.

Functions

• Functions can encapsulate an expression.

• Functions can be stored in variables.

• Functions may have parameters.

• Functions can be invoked.

• Functions can grow the language.

function (parameter) { return expression;}double = function (number) { return number * 2;}

double(212)

function (parameter) { return expression;}celsius = function (f) { return (f - 32) * 5 / 9;}

boiling_point = celsius(212)

function (parameter) { return expression;}

quad = function (x) { return double(x) + double(x);}

average = function (a, b) { return (a + b) / 2; }

Functions

• A function can take many parameters, or no parameters.

• If it takes more than one parameter, the parameter names are separated with commas.

• A parameter name is like a variable inside the function.

• When a function is called, the argument values are assigned to the parameters.

Assignment One

1. Read Preface, Chapter One of The Good Parts

2. Write function fahrenheit(c)

3. Write a function of your own that takes two or more parameters.

4. Using trial and error, determine the temperature such that

fahrenheit(x) === celsius(x)

Put your answers in a text or html file and add it to http://groups.yahoo.com/group/jsmvhs/files/Assignment1/

Use your unique ID in the name of the file.