Software Design by Example: A Tool-Based Introduction with JavaScript

Cover....1

Half Title....2

Title Page....4

Copyright Page....5

Dedication....6

Contents....8

1. Introduction....12

1.1. Who is our audience?....12

1.2. What tools and ideas do we cover?....13

1.3. How are these lessons laid out?....14

1.4. How did we get here?....14

1.5. How can people use and contribute to this material?....15

1.6. Who helped us?....16

2. Systems Programming....18

2.1. How can we list a directory?....19

2.2. What is a callback function?....20

2.3. What are anonymous functions?....23

2.4. How can we select a set of files?....24

2.5. How can we copy a set of files?....27

2.6. Exercises....30

3. Asynchronous Programming....34

3.1. How can we manage asynchronous execution?....34

3.2. How do promises work?....37

3.3. How can we chain operations together?....38

3.4. How are real promises different?....40

3.5. How can we build tools with promises?....42

3.6. How can we make this more readable?....45

3.7. How can we handle errors with asynchronous code?....47

3.8. Exercises....48

4. Unit Testing....52

4.1. How should we structure unit testing?....52

4.2. How can we separate registration, execution, and reporting?....53

4.3. How should we structure test registration?....54

4.4. How can we build a command-line interface for testing?....57

4.5. Exercises....59

5. File Backup....64

5.1. How can we uniquely identify files?....64

5.2. How can we back up files?....67

5.3. How can we track which files have already been backed up?....70

5.4. How can we test code that modifies files?....72

5.5. Exercises....76

6. Data Tables....80

6.1. How can we implement data tables?....81

6.2. How can we test the performance of our implementations?....84

6.3. What is the most efficient way to save a table?....86

6.4. Does binary storage improve performance?....87

6.5. Exercises....89

7. Pattern Matching....94

7.1. How can we match query selectors?....94

7.2. How can we implement a simple regular expression matcher?....98

7.3. How can we implement an extensible matcher?....100

7.4. Exercises....108

8. Parsing Expressions....110

8.1. How can we break text into tokens?....111

8.2. How can we turn a list of tokens into a tree?....114

8.3. Exercises....119

9. Page Templates....122

9.1. What will our system look like?....123

9.2. How can we keep track of values?....124

9.3. How do we handle nodes?....125

9.4. How do we implement node handlers?....128

9.5. How can we implement control flow?....132

9.6. How did we know how to do all of this?....134

9.7. Exercises....135

10. Build Manager....138

10.1. What’s in a build manager?....139

10.2. Where should we start?....139

10.3. How can we specify that a file is out-of-date?....144

10.4. How can we update out-of-date files?....145

10.5. How can we add generic build rules?....147

10.6. What should we do next?....153

10.7. Exercises....153

11. Layout Engine....156

11.1. How can we size rows and columns?....157

11.2. How can we position rows and columns?....160

11.3. How can we render elements?....162

11.4. How can we wrap elements to fit?....165

11.5. What subset of CSS will we support?....167

11.6. Exercises....172

12. File Interpolator....176

12.1. How can we evaluate JavaScript dynamically?....176

12.2. How can we manage files?....180

12.3. How can we find files?....182

12.4. How can we interpolate pieces of code?....184

12.5. What did we do instead?....186

12.6. Exercises....186

13. Module Loader....190

13.1. How can we implement namespaces?....190

13.2. How can we load a module?....192

13.3. Do we need to handle circular dependencies?....193

13.4. How can a module load another module?....196

13.5. Exercises....199

14. Style Checker....202

14.1. How can we parse JavaScript to create an AST?....202

14.2. How can we find things in an AST?....204

14.3. How can we apply checks?....206

14.4. How does the AST walker work?....207

14.5. How else could the AST walker work?....209

14.6. What other kinds of analysis can we do?....212

14.7. Exercises....215

15. Code Generator....218

15.1. How can we replace a function with another function?....218

15.2. How can we generate JavaScript?....220

15.3. How can we count how often functions are executed?....222

15.4. How can we time function execution?....224

15.5. Exercises....226

16. Documentation Generator....230

16.1. How can we extract documentation comments?....230

16.2. What input will we try to handle?....233

16.3. How can we avoid duplicating names?....237

16.4. Code is Data....241

16.5. Exercises....242

17. Module Bundler....244

17.1. What will we use as test cases?....244

17.2. How can we find dependencies?....246

17.3. How can we safely combine several files into one?....250

17.4. How can files access each other?....252

17.5. Exercises....257

18. Package Manager....260

18.1. What is semantic versioning?....260

18.2. How can we find a consistent set of packages?....261

18.3. How can we satisfy constraints?....263

18.4. How can we do less work?....265

18.5. Exercises....269

19. Virtual Machine....272

19.1. What is the architecture of our virtual machine?....272

19.2. How can we execute these instructions?....274

19.3. What do assembly programs look like?....277

19.4. How can we store data?....281

19.5. Exercises....283

20. Debugger....286

20.1. What is our starting point?....286

20.2. How can we make a tracing debugger?....288

20.3. How can we make the debugger interactive?....292

20.4. How can we test an interactive application?....294

20.5. Exercises....299

21. Conclusion....302

A. License....304

B. Code of Conduct....308

C. Contributing....310

D. Bibliography....312

E. Glossary....314

Index....336

The best way to learn design in any field is to study examples, and some of the best examples of software design come from the tools programmers use in their own work. Software Design by Example: A Tool-Based Introduction with JavaScript therefore builds small versions of the things programmers use in order to demystify them and give some insights into how experienced programmers think. From a file backup system and a testing framework to a regular expression matcher, a browser layout engine, and a very small compiler, we explore common design patterns, show how making code easier to test also makes it easier to reuse, and help readers understand how debuggers, profilers, package managers, and version control systems work so that they can use them more effectively.

This material can be used for self-paced study, in an undergraduate course on software design, or as the core of an intensive weeklong workshop for working programmers. Each chapter has a set of exercises ranging in size and difficulty from half a dozen lines to a full day’s work. Readers should be familiar with the basics of modern JavaScript, but the more advanced features of the language are explained and illustrated as they are introduced.

All the written material in this project can be freely reused under the terms of the Creative Commons - Attribution license, while all of the software is made available under the terms of the Hippocratic License. All proceeds from sale of this book will go to support the Red Door Family Shelter in Toronto.

Features

• Teaches software design by showing programmers how to build the tools they use every day
• Each chapter includes exercises to help readers check and deepen their understanding
• All the example code can be downloaded, re-used, and modified under an open license