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Before you start No programming experience needed. Begin with values, basic strings, and arrays; the later chapters build toward asynchronous work and data validation.

1. Your first JavaScript programBeginner
2. Values and decisionsBeginner
3. Strings you can read and changeBeginner
4. Arrays and the first itemBeginner
5. Functions and loop boundariesBeginner
6. Objects with named propertiesBeginner
7. Destructuring, defaults, and rest parametersIntermediate
8. Transform collections without surprisesIntermediate
9. Object identity and deliberate nested updatesIntermediate
10. Closures and keyed stateIntermediate
11. Methods, receivers, and class invariantsIntermediate
12. Modules and explicit dependenciesIntermediate
13. Promises and failure pathsAdvanced
14. Concurrent promises and result orderingAdvanced
15. Text, Unicode, and explicit normalizationIntermediate
16. Recursive decomposition and search invariantsAdvanced
17. Validate data at boundariesAdvanced

Before you start No programming experience needed. Start with your first program, then strings, lists, decisions, and small functions before the deeper topics.

1. Your first Python programBeginner
2. Working with stringsBeginner
3. Lists and changing one itemBeginner
4. Decisions and repeating workBeginner
5. Functions that return an answerBeginner
6. Values, text, and arithmeticBeginner
7. Functions and dependable defaultsBeginner
8. Lists, sets, and dictionariesIntermediate
9. Comprehensions and nested aliasingIntermediate
10. Lexical scope and closuresIntermediate
11. Iterators and lazy pipelinesIntermediate
12. Instance state and behavioral contractsIntermediate
13. Exceptions and resource boundariesAdvanced
14. JSON parsing and domain validationAdvanced
15. Records, ordering, and invariantsAdvanced
16. Modules and tests that challenge a contractIntermediate
17. Recursive algorithms and terminating rangesAdvanced

Before you start No previous Java required. Intro to Java explains how a small program runs; objects, types, methods, and collections are introduced as you progress.

1. Intro to JavaBeginner
2. Using objectsBeginner
3. Data typesBeginner
4. ClassesIntermediate
5. DecisionsBeginner
6. IterationIntermediate
7. Arrays and ArrayListsIntermediate
8. Sorting and searchingIntermediate
9. Designing classesIntermediate
10. Interfaces and polymorphismAdvanced
11. InheritanceAdvanced
12. Exception handlingAdvanced
13. RecursionAdvanced

Before you start No SQL experience needed. Begin by reading a table and selecting columns. Later chapters introduce joins, grouping, windows, and recursive queries using SQLite.

1. Read a table and choose columnsBeginner
2. Select rows with a clear orderBeginner
3. Missing values and three-valued logicBeginner
4. Keys, constraints, and valid rowsIntermediate
5. Join tables without losing the questionIntermediate
6. Existence tests and correlated questionsIntermediate
7. Aggregate at the right grainIntermediate
8. Set operations and duplicate meaningIntermediate
9. CTEs and windowed analysisAdvanced
10. Dates, ranges, and deterministic periodsIntermediate
11. Recursive CTEs and terminationAdvanced
12. Updates, upserts, and affected rowsAdvanced
13. Transactions, constraints, and query plansAdvanced
14. Indexes and evidence-based query tuningAdvanced

Before you start No previous C# required. Start with a small program, then values and arrays before methods, classes, and asynchronous work.

1. Run and read a C# programBeginner
2. Values, types, and stringsBeginner
3. Create and read an arrayBeginner
4. Decisions, loops, and methodsBeginner
5. Arrays, value copies, and shared referencesIntermediate
6. Pattern matching and exhaustive decisionsIntermediate
7. Classes, properties, and invariantsIntermediate
8. Collections and LINQ pipelinesIntermediate
9. Dictionary contracts and equality rulesIntermediate
10. Delegates and captured stateIntermediate
11. Iterator methods and deferred executionAdvanced
12. Interfaces and virtual behaviorAdvanced
13. Nullable values and explicit failuresIntermediate
14. Deterministic cleanup with usingAdvanced
15. Tasks, asynchronous completion, and failureAdvanced

Before you start Bring basic JavaScript variables, functions, arrays, and object literals. Classes are taught later; you do not need to finish the whole JavaScript course first.

1. Read compiler feedback and run a checked programIntermediate
2. Types as working contractsBeginner
3. Object shapes and readonly viewsBeginner
4. Tuples, rest parameters, and array boundariesIntermediate
5. Narrowing and explicit statesIntermediate
6. Literal inference and checked configurationIntermediate
7. Preserve relationships with genericsIntermediate
8. Function compatibility and callback promisesAdvanced
9. Classes, structural contracts, and private stateIntermediate
10. Module boundaries and type-only dependenciesIntermediate
11. Typed asynchronous results and explicit failureAdvanced
12. Derive API types from one modelAdvanced
13. Conditional types and union distributionAdvanced
14. Unknown input and trustworthy resultsAdvanced