Welcome to JS

The best authors and the best JavaScript developers are those who obsess about language, who explore and experiment with language every day and in doing so develop their own style, their own idioms, and their own expression.

— Angus Croll, If Hemingway Wrote JavaScript

Take your first steps into programming by learning to read, trace, analyze, and write interactive programs in your browser.

By the end of this module using Just Enough JavaScript you will be able to document, plan and develop programs that process a user's text input.

• Learning Objectives: what you can expect to learn from studying this material
• Setting Up: how to set up and study this material
• Suggested Study: Helpful links for this module, useful but not required.
  • Flashcards: Study these a little bit every day and add new flashcards for things you don't want to forget.
  • Printables: Cheat sheets and diagrams you can print out and have next to you while studying.
• Study Tips: Some tips for getting the most out of your time learning to program.
• Lesson Plans: A few ideas for running lessons around this material.

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Learning Objectives

all of these skills are limited to short, single-page programs written with Just Enough JavaScript

Priorities: 🥚, 🐣, 🐥, 🐔 (click to learn more)

There is a lot to learn in this repository. If you can't master all the material at once, that's expected! Anything you don't master now will always be waiting for you to review when you need it. These 4 emoji's will help you prioritize your study time and to measure your progress:

• 🥚: Understanding this material is required, it covers the base skills you'll need for this module and the next. You do not need to finish all of them but should feel comfortable that you could do them with enough time.
• 🐣: You have started all of these exercises and feel you could complete them all if you just had more time. It may not be easy for you but with effort you can make it through.
• 🐥: You have studied the examples and started some exercises if you had time. You should have a big-picture understanding of these concepts/skills, but may not be confident completing the exercises.
• 🐔: These concepts or skills are not necessary but are related to this module. If you are finished with 🥚, 🐣 and 🐥 you can use the 🐔 exercises to push yourself without getting distracted from the module's main objectives.

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1. What is Programming

What is a program? What is a programming language? How do programs and people fit together?

• 🥚 Data in, Data Out: You understand that computer programs are used to transform data, and can explain a JS program from this module in terms of the data that goes in and the data that comes out.
• 🥚 Three Audiences: You can explain how a single file of code is used to communicate with 3 different audiences:
  • Developers: You can explain how code formatting, comments, logs and variable names make it easier (or harder!) for a developer to understand a program.
  • Computers: You can explain how a computer follows your instructions to store, read and modify data in program memory.
  • Users: You can explain how the computer creates a dynamic user experience by following different executions paths depending on user input.
• 🥚 Tracing Variables: You can complete a trace table for a program that uses only variables, and can check your work using the "trace" button.

2. Just Enough JavaScript

Go in depth on JavaScript you need to know for writing interactive text-based programs in the browser. Along the way you will learn how each language feature works in small programs.

• 🥚 JavaScript Syntax: Given a program, you can identify these parts of JavaScript syntax:
  • Primitives
  • Operators
  • Identifiers
  • Keywords
  • Checks
  • Blocks
  • Function Calls
• 🥚 Listening and Reading: You can read code out loud, and understand your classmates when they read code to you. You don't need to understand how a program works to master these learning objectives!
  • Listening You can exactly re-write a program that a classmate has read
  • Reading You can read a program out loud and guide your classmates to re-write exactly the same code without them seeing the program. Every indentation, semi-colon, comment and spelling in their program must be identical to yours.
• 🥚 Static vs. Dynamic Analysis: You can explain and use these two ways of studying a program, each can help you understand different aspects of your code. To help understand this concept, the options panel in Study Lenses is organized into static and dynamic study options:
  • Static: Studying the text in a code file without running it. Some static study methods are creating a flowchart, analyzing variables, filling out a trace table, and drawing on code.
  • Dynamic: Running code and studying the computer's behavior. Some dynamic study methods are running code and reading console logs, using the trace button, and stepping through in the debugger or JS Tutor.
• 🥚 Tracing Execution: You can complete a "steps" trace table for all JS language features in Just Enough JavaScript, and can correct your table using console output from the "trace" button.
• 🥚 Analyzing Variables: You can list all the variables in a program, and answer these 5 questions for each variable:
  • Where is the variable declared?
  • What is the variable's scope?
  • Is the variable initialized with a value?
  • How many times is its value used (read) in the program?
  • How many times is the variable assigned a new value?
  • What types are assigned to this variable during the program's execution?
• 🥚 Completing Programs: You can successfully fill in blanks for a program when the missing words are provided, including distractors.
• 🐣 Translating Pseudo Code: Given a program written in Pseudo Code, you can translate it to working JavaScript.
• 🐣 Comparing Programs: You can compare two programs with similar code and explain if they have the same behavior or not. If they do not, you can explain how they behave differently and why.
• 🐥 Constructing Programs: You can reconstruct a program's lines and indentation, successfully ignoring distractor lines.

3. Understanding Programs

Learn how to understand a larger programs by finding connections between the details and the big picture. By the end of this chapter you will know how to read a new program and do a simple code review.

• 🥚 Stepping Through: You can pause a script in a your browser's debugger, arrange the debugger, collapse extra panels, and step through a script written with Just Enough JS. At each point in execution you can make a prediction of the next line before executing, and can check your prediction using the scopes panel.
• 🥚 Imperative Programming: You can explain what the Imperative Programming paradigm is, and can explain how you know the programs in Welcome to JS are Imperative.
• 🥚 Program Goals: You understand that a full JavaScript program can be explained as a series of smaller goals, and can write names for the goals in a simple working program.
• 🥚 Logging: You can tracing specific aspects of a program's execution and log them to the console.
• 🐣 Tracing Backwards You can trace backwards from a program's output to it's input.
• 🐣 Naming Variables: You can analyze how a variable is used in a program and give it two names:
  • Generic: You can give a generic name to a variable based on how it is used in the program.
  • Specific: You can give a specific name to a variable based on how it's used and the program's domain (the program's specific data and use-case).
• 🐣 Describing Programs: You can read a program and describe it with comments using to the methodology from /describing-programs:
  1. Zoom Out
  2. Zoom In
  3. Find Connections
  4. Describe Goals
• 🐣 Code Review: Given a working program you can review the code for clarity, correctness and style.

4. Developing Programs

Learn to modify and write larger programs in JavaScript. You'll cover many of the hidden skills necessary to develop quality software and to work collaboratively on a code base.

• 🥚 Linting: You can find and fix simple linting errors in JavaScript programs.
• 🥚 Program Life Cycle: You can explain the two phases of a program's life cycle.
  1. Creation Phase
  2. Execution Phase
• 🥚 Fixing Errors: You can use the structured comment to describe an error in your program, and can make several educated guesses at how to fix the error.
• 🐣 Fixing Bugs: You can use the structured comment to describe and fix a bug in small programs.
• 🐣 Modifying Programs: You can make small changes in a program to change its behavior without breaking it.
• 🐥 Refactoring: Given a working program, you can make changes to the code without changing the program's user-facing behavior.
• 🐥 Legacy Code: You can understand and rewrite a poorly written program to improve the experience of all 3 audiences: developer, user, computer.
• 🐥 Writing Programs: Given a description of a program's behavior (user story + test cases), you can plan goals for the program and write code to pass the tests.
• 🐔 Reverse Engineering: Given a working program with unreadable code, you can:
  • Give the program a name.
  • Describe the program's behavior with a user story, acceptance criteria and test cases.
  • Plan goals for the program.
  • Develop your own working program with the exact same behvior.
• 🐔 Imagining Programs: Given an empty page, you can imagine and develop your own programs using Just Enough JavaScript. This includes:
  • A title.
  • A description with a user story, acceptance criteria and test cases.
  • Commented goals.
  • Fully working Code.

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Setting Up

expand/collapse

You will need NPM and nvm on your computer to study this material

Using a browser with good DevTools will make your life easier: Chromium, FireFox, Edge, Chrome

1. Install or update the study-lenses package globally
   • $ npm install -g study-lenses (if you do not have it installed)
   • $ npm update -g study-lenses (if you already have it installed)
   • Didn't work? you may need to try:
     • (mac) $ sudo npm install -g study-lenses
   • having trouble updating?
     • try this: $ npm uninstall -g study-lenses && npm install -g study-lenses
2. Fork and clone this repository:
   1. fork the HackYourFuture repository to your personal account
      • git@github.com:HackYourFutureBelgium/welcome-to-js.git
   2. clone your fork to your computer
      • git clone --depth 1 git@github.com:HackYourFutureBelgium/<your-user-name>.git
   3. when there are updates to the module:
      1. update your fork with a PR
      2. pull the changes from your fork to your computer
3. Navigate to the module repository in terminal
   • $ cd welcome-to-js
4. Run the lenses2 command from your CLI
   • $ lenses2
5. The material will open in your default browser, you're good to go!
   • you can read the study-lenses user guide from your browser by navigating to localhost:xxxx?--help

If you have a Windows computer and get this error:

• ... /study.ps1 cannot be loaded because running scripts ...

follow the instructions in this StackOverflow answer, that should take care of it ; )

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Code Quality Scripts

This repository comes with some scripts to check the quality of this code. You can run these scripts to check the code provided by HYF, and to check the code you write when experiment with the examples and complete the exercises.

npm run format

This script will format all of the code in this repository making sure that all the indentations are correct, the code is easy to read, and letting you know if there are any syntax errors.

npm run spell-check

This script will check all of the files in your repository for spelling mistakes. Spelling is not just a detail, is important! Good spelling helps others read and understand your programs with less effort.

spell-check is not so clever though, it doesn't have all possible words in it's dictionary and it won't know if you wanted to spell a word incorrectly. If you think one of it's "Unknown word"s is not a problem, you can either ignore the suggestion or add the word to the "words": [ ... ], list in .cspell.json.

npm run lint:md

This script will lint all the Markdown files in this repository, checking for syntax mistakes and other bad practices. Fixing linting errors will help you learn to write better code by pointing out your mistakes before they cause problems in your program.

Some linting errors will take some practice to understand and fix, but it will be a good use of time.

npm run lint:js -- ./path/to/code

Just like lint:md, but for .js files. This script will lint all of the JS files in this repository, letting you know if there are any syntax errors or bad practices.