Inside JS

Learning Objectives

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 to move on. You do not need to finish all of them but should feel comfortable that you could 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.

0. Asserting

Skills:
- 🥚 Predicting Execution: You can use the browser's debugger to step through your code. Before each step you can make a prediction about what will happen, after each step you can check your prediction.
- 🥚 Assertion Testing: You can write assertion tests to predict what values will be in your program at a specific step of execution.
Language Features
- 🥚 Comments: You can write clear, helpful comments and can explain different ways comments can be used in a program.
- 🥚 Strings: You can write and read string values in a program.
- 🥚 let vs. const: You can explain the differences between let and const including: uninitialized declarations and reassignment. You can determine when a variable can be assigned with const in a program.
- 🥚 Strict Comparison: You can explain how the === and !== operators compare strings, and can predict the result of any string comparison.
- 🥚 console.log: You can use console.log to create program traces in the console, and to print other helpful info for developers.
- 🥚 console.assert: You can use the console.assert for assertion testing, and can write a helpful message assertion message.

1. Primitives and Operators

Skills:
- 🥚 Predicting Truthiness: You can predict the truthiness of any primitive value.
- 🐣 Tracing Operators: You can use an operators trace table to evaluate expressions with more than one operator, and you can check your work with the [trace] button.
Language Features
- 🥚 Primitive Types: You can explain the difference between the 5 main primitive types (string, number, boolean, null, undefined) and what they are used for in a program.
- 🥚 typeof: You can predict the typeof operator's output for values from any of the 5 main primitive types.
- 🥚 Explicit Coercion: You can predict & check the outputs when using Boolean(), String() and Number() to convert between primitive types.
- 🥚 Truthiness Operators: You can explain how truthiness is used when evaluating &&, ||, ! and ? :.
- 🐣 Short-Circuiting: You can write an example that demonstrates how short-circuiting works with && and ||.
- Implicit Coercion:
  - 🐣 You can explain what implicit coercion is and how it can cause problems in your programs.
  - 🐣 You can explain the rules for implicit coercion in common operators such as +, ! and >.
- 🐣 Comparisons: You can predict and check the result of any primitive comparison.
- 🐣 Template Literals: You can read and trace multi-line template literal strings.
- 🐥 Statements vs. Expressions: You can identify if a piece of code is a statement or an expression.
- 🐔 Arithmetic: You can use JavaScript to do math, and can explain or debug your expressions when they evaluate to something unexpected.

2. Just Enough DOM

Skills:
- 🥚 Event-Driven Programming: You can explain and discuss this programming paradigm in terms of the user interface, user interactions, and processing user input.
- 🐣 Entry Points: You can explain the concept of program entry points by describing which lines of code are executed when a program is loaded, and which lines of code are executed when a user takes an action.
- 🐣 Program Structure: You can understand and modify programs using the structure described in /02-just-enough-dom - imports, description, constants, state, DOM elements, interactions, initialization.
Language Features: You are comfortable reading, tracing, and completing programs that use ...
- 🥚 document.getElementById(''): You can access a single DOM element using it's unique ID attribute, and save it to a variable for use in your program.
- 🥚 checkbox.checked: You can read a boolean value from inputs with type="checkbox".
- 🥚 Number(numberInput.value): You can read a string value from inputs with type="number" and cast the value to type number in your program.
- 🥚 otherInput.value: You can read a string value from all other input types.
- 🥚 pre.innerText: You can display a formatted string in the DOM by assigning to a <pre> element's .innerText property.
- 🐣 element.addEventListener('input'/'click', () => {}): You can define what code should be executed when a user interacts with a specific element. You do not need to completely understand this syntax or how functions work, it's enough if you can complete the exercises in this chapter. (You'll learn about functions later on, then it will all make sense.)

3. Control Flow

Skills:
- 🥚 Imperative Programming: You can define the imperative programming paradigm and can explain how you know the programs in this chapter are imperative.
- Writing Interactive Programs: For programs that take a string from users:
  - 🥚 Blanks: You can complete a program by filling in the blanks.
  - 🐣 Bugs: You can fix bugs in an otherwise complete program.
  - 🐣 Goals: You can write the missing portion of a program.
  - 🐔 Empty Page: You can develop a program with specific behavior starting from an empty page.
- 🐥 User Numbers: You can complete, debug and write programs that cast user input from string to number.
- 🐥 Stateful Programs: You can step through, debug and complete programs with an HTML/CSS interface that store user data in a variable between interactions.
- Refactoring Control Flow:
  - 🐥 Conditionals: You can refactor between truthiness operators and if/else statements.
  - 🐥 Loops: You can either refactor between all loop types, or explain when it is not possible (or a good idea).
Language Features: You are comfortable reading and tracing programs that use ...
- 🥚 Block Scope: You can show how block scope works using code snippets and your browser's debugger.
- 🥚 Conditionals: You can predict and trace a program's path through conditional statements.
- 🥚 While Loops: You can predict and trace simple programs that use while loops.
- 🥚 for-of Strings: You can predict and trace simple programs that iterate through the characters of a string using for-of.
- 🥚 For Loops: You can explain how a for loops works by refactoring simple for loops into while loops.
- 🐣 Break: You can predict and trace simple programs that use break.
- 🐣 Continue: You can predict and trace simple programs that use continue.

4. Functions

Skills:
- 🥚 Tracing: You can use the debugger to predict and check the execution of small programs that use functions. This includes:
- 🥚 Test Cases: You can explain a simple function's behavior using inputs & outputs.
- 🐣 Documenting Functions: You can write a JS Doc comment to describe a function's behavior, inputs and outputs.
Language Features:
- 🥚 ES6 Arrow Functions:
  - Defining a Function: You can show where a function is defined in a program.
  - Parameters: You can find a function's parameters in it's definition
  - Return Statement: You can find the return statements in a function's definition.
  - Calling a Function: You can show where a function called in a program
  - Arguments: You can show the arguments passed to a function call.
  - Return Value: You can show how a function's return value is used after the function call.
- 🥚 Default Parameters: You can explain how default parameters work, and how they help a developer read/understand a function definition.
- 🐣 The Callstack: You can explain and inspect the callstack using the browser's debugger.
- 🐥 Variables in Functions: You can explain three different ways a variable in a function can be declared/assigned, and can show this in the debugger:
  1. Parameters: A parameter is assigned it's value when a function is called with arguments.
  2. Local Variables: A variable declared in the function's curly braces.
  3. Parent Scope Variables: A variable that was declared outside of the function but used inside the function (avoid this for now.)

5. Unit Testing

Skills:
- 🥚 Testing Environments: You understand that the conventional describe/it/expect.toEqual functions are defined by a testing library and made available as global variables in a testing environment. They are not part of JavaScript!
- 🥚 File Sub-Extensions: You can identify how a file is used by it sub-extension: file.__.js. Sub-extensions are a convention for developers and development tools. They do not change how JavaScript inside the file works.
- 🥚 Reading Tests: You can read unit tests to understand what a function is supposed to do.
- 🥚 Stepping Through Tests: You can step through unit tests in the debugger, stepping over the global testing functions and into the function you are testing.
- 🐣 Writing Tests: Given a working function, you can write passing unit tests to describe it's behavior.
- 🐣 Debugging Functions: Given working tests and a function with small mistakes, you can use the tests as a guide while debugging the function.
- 🐥 Passing Tests: Given working unit tests and an empty function, you can write code to pass the tests.
Language Features:
- nothing new here!

6. ES Modules

Skills:
- 🥚 Spec Files: You can work with functions and unit tests separated into two files.
- 🥚 Visualizing Dependencies: You can use the VSCode Dependency Cruiser extension and the ?deps lens to visualize the dependencies in a folder.
- 🐣 Refactoring Tests: You can refactor a function and unit tests from one file to two files: one with the function, one with the unit tests.
Language Features:
- 🥚 Module Files: Are always in strict mode by default, no more 'use strict'!
- 🥚 Named Exports: You can export a variable and it's value using export const _ = () => {};
- 🥚 Named Imports: You can import a variable and it's value from another file using import { _ } from './path/to/file.js';
- 🐥 Module Life-Cycle: You understand that ES Modules are static, and are evaluated at creation phase.

7. Using Functions

Skills:
- 🥚 Procedural Programming: You can define the procedural programming paradigm and can explain how you know the programs in this chapter are procedural.
- 🥚 Using Functions: You can use a pre-written functions in a program.
- 🐣 Writing Functions: You can write functions that are used in a program.
- 🐥 Refactoring Functions: You can refactor a function out of a program and test the function separately.
- 🐔 Reverse-Engineering: You can reverse-engineer an example program and refactor parts of your program into separate functions.
Language Features:
- Nothing new here!

8. Arrays

Skills:
- 🥚 Reference vs. Value: You can explain how arrays are stored in memory and can demonstrate using examples run in JS Tutor.
- 🥚 Deep vs. Shallow Comparison: You can explain use the concept of reference vs. value to explain how a deep comparison is different than a shallow comparison.
- Side-Effects: You can ...
  - 🥚 Explain what side-effects are with an example.
  - 🥚 Avoid side effects when writing your own functions.
  - 🐣 Write tests to check if a function has side-effects.
  - 🐣 Fix side-effects in buggy functions.
- Integrating Arrays: You can work with programs that use arrays to store user data:
  - 🥚 Call: You can call pre-written functions in a program:
  - 🐣 Write: You can write functions that are used in a pre-written program.
  - 🐣 Refactor: You can refactor logic from a program into a separate function. You can avoid side-effects and test your function.
  - 🐔 Reverse-Engineer: You can reverse-engineer a program, refactoring logic to a separate function if necessary.
- 🐥 Stateful Programs: You can step through, debug and complete programs with an HTML/CSS interface that store user data in an array between interactions.
Language Features: You are comfortable reading and tracing programs that use ...
- 🥚 Array Literals: You can create a new array in your program with initial values using the array literal syntax: const arr = ['items'];
- 🥚 Adding and Removing Items: You can use these methods to add and remove items in an array:
  - arr.push(): Adds a new item to the end of an array.
  - arr.pop(): Removes the last item in an array.
  - arr.shift(): Removes the first item in an array.
  - arr.unshift(): Adds a new item to the front of an array.
- 🥚 Reading Items: You can read items in an array using:
  - arr[i]: Access a specific item in an array using square brackets a positive index.
  - arr.at(i): Access a specific item in an array using .at() and a positive or negative index.
- 🥚 Updating Items: You can update any item in an array using it's index, square brackets and assignments: arr[4] = 'hello'.
- 🥚 Iterating Over Arrays:
  - for (const item of arr): You use for-of loops to iterate forwards through an array.
  - for (let i = ...): You can use for loops to iterate forwards and backwards through an array.
- 🥚 Array.isArray(): You can use Array.isArray() to check if something is an array: Array.isArray(something)
- 🥚 Spread Syntax: you can use spread syntax to create a shallow copy of an array: const shallowCopy = [...arr];

9. Functional Array Methods

Skills:
- 🥚 Declarative Programming: You can define the declarative programming paradigm and can explain how you know that code using functional array methods is declarative.
- 🥚 Array Strategies: You can explain these array strategies using a diagram or drawing:
  - Mapping: Modifying each item in an array and putting the results in a new array.
  - Filtering: Creating a new array with only the items from the old array that match some criteria.
  - Every Item: Checking if every item in an array matches some criteria.
  - Some Items: Checking if at least one item in an array matches some criteria.
  - Finding: Finding the first item in an array that matches some criteria.
  - Reducing: Combining all the items in an array to create a single result.
- 🐣 Using Callbacks: You can explain what a callback is, and can ...
  - Pass a callback into a higher-order function that consumes it.
  - Write a callback for a higher-order function to consume.
  - Consume callbacks in a higher-order function that you write.
  - Decide when to declare callbacks inline, and when to declare them separately.
- 🐣 Debugging Functional Array Methods: You can step through code that uses functional array methods in your debugger, and can use the scopes panel to explain what is happening behind the scenes.
Language Features:
- Array Methods: You can read and trace code that uses these array methods, you can also use them to solve simple coding challenges:
  - 🥚 [].every
  - 🥚 [].some
  - 🐣 [].map
  - 🐣 [].filter
  - 🐣 [].find
  - 🐥 [].reduce
- 🐣 Higher-Order Functions: You can explain what a higher order function is using a simple example.
- 🐥 Implicit Returns: You understand when a function can be written with an implicit return and can decide if it makes your code more or less readable.

10. Multiple Interactions

Skills:
- 🥚 Avoiding Side Effects: You can read, debug and write functions that use objects as arguments, without creating side-effects.
- 🐣 Stateful Programs: You can step through, debug and complete programs with an HTML/CSS interface that store user data in an object between interactions.
Language Features:
- 🥚 Object Literals: You can declare a new object with initial key/value pairs using object literal syntax: const obj = { a: 1, b: 2 };.
- 🐣 Dots vs. Brackets: You can explain the difference between dot and bracket access in an object and can decide which one is best in your code.
- 🐣 Reference vs. Values: You can show that objects are stored by reference with an example that modifies one object from two variables.

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