- Introduction
- Chapter 1 Values, Types, and Operators
- Chapter 2 Program Structure
- Expressions and statements
- Variables
- Keywords and reserved words
- The environment
- Functions
- The console.log function
- Return values
- prompt and confirm
- Control flow
- Conditional execution
- while and do loops
- Indenting Code
- for loops
- Breaking Out of a Loop
- Updating variables succinctly
- Dispatching on a value with switch
- Capitalization
- Comments
- Summary
- Exercises
- Chapter 3 Functions
- Chapter 4 Data Structures: Objects and Arrays
- Chapter 5 Higher-Order Functions
- Chapter 6 The Secret Life of Objects
- Chapter 7 Project: Electronic Life
- Chapter 8 Bugs and Error Handling
- Chapter 9 Regular Expressions
- Creating a regular expression
- Testing for matches
- Matching a set of characters
- Repeating parts of a pattern
- Grouping subexpressions
- Matches and groups
- The date type
- Word and string boundaries
- Choice patterns
- The mechanics of matching
- Backtracking
- The replace method
- Greed
- Dynamically creating RegExp objects
- The search method
- The lastIndex property
- Parsing an INI file
- International characters
- Summary
- Exercises
- Chapter 10 Modules
- Chapter 11 Project: A Programming Language
- Chapter 12 JavaScript and the Browser
- Chapter 13 The Document Object Model
- Chapter 14 Handling Events
- Chapter 15 Project: A Platform Game
- Chapter 16 Drawing on Canvas
- Chapter 17 HTTP
- Chapter 18 Forms and Form Fields
- Chapter 19 Project: A Paint Program
- Chapter 20 Node.js
- Chapter 21 Project: Skill-Sharing Website
- Eloquent JavaScript
- Exercise Hints
- Program Structure
- Functions
- Data Structures: Objects and Arrays
- Higher-Order Functions
- The Secret Life of Objects
- Project: Electronic Life
- Bugs and Error Handling
- Regular Expressions
- Modules
- Project: A Programming Language
- The Document Object Model
- Handling Events
- Project: A Platform Game
- Drawing on Canvas
- HTTP
- Forms and Form Fields
- Project: A Paint Program
- Node.js
- Project: Skill-Sharing Website
Modules
Beyond the few variables I mentioned, such as console
and process
, Node puts little functionality in the global scope. If you want to access other built-in functionality, you have to ask the module system for it.
The CommonJS module system, based on the require
function, was described in Chapter 10 . This system is built into Node and is used to load anything from built-in modules to downloaded libraries to files that are part of your own program.
When require
is called, Node has to resolve the given string to an actual file to load. Pathnames that start with "/"
, "./"
, or "../"
are resolved relative to the current module’s path, where "./"
stands for the current directory, "../"
for one directory up, and "/"
for the root of the file system. So if you ask for "./world/world"
from the file /home/marijn/elife/run.js
, Node will try to load the file /home/marijn/elife/world/world.js
. The .js
extension may be omitted.
When a string that does not look like a relative or absolute path is given to require
, it is assumed to refer to either a built-in module or a module installed in a node_modules
directory. For example, require("fs")
will give you Node’s built-in file system module, and require("elife")
will try to load the library found in node_modules/elife/
. A common way to install such libraries is by using NPM, which I will discuss in a moment.
To illustrate the use of require
, let’s set up a simple project consisting of two files. The first one is called main.js
, which defines a script that can be called from the command line to garble a string.
var garble = require("./garble"); // Index 2 holds the first actual command-line argument var argument = process.argv[2]; console.log(garble(argument));
The file garble.js
defines a library for garbling strings, which can be used both by the command-line tool defined earlier and by other scripts that need direct access to a garbling function.
module.exports = function(string) { return string.split("").map(function(ch) { return String.fromCharCode(ch.charCodeAt(0) + 5); }).join(""); };
Remember that replacing module.exports
, rather than adding properties to it, allows us to export a specific value from a module. In this case, we make the result of requiring our garble
file the garbling function itself.
The function splits the string it is given into single characters by splitting on the empty string and then replaces each character with the character whose code is five points higher. Finally, it joins the result back into a string.
We can now call our tool like this:
$ node main.js JavaScript Of{fXhwnuy
This is a book about getting computers to do what you want them to do. Computers are about as common as screwdrivers today, but they contain a lot more hidden complexity and thus are harder to operate and understand. To many, they remain alien, slightly threatening things.
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