Asynchronous JavaScript

  1. The Promise API
    1. Introduction to Promises
      1. Definition and Purpose
        1. A Placeholder for a Future Value
          1. Solving Callback Hell
            1. Flattening Asynchronous Code
              1. Improved Error Handling
            2. Promise States
              1. Pending
                1. Initial State
                  1. Characteristics and Behavior
                  2. Fulfilled
                    1. Successful Completion
                      1. Value Resolution
                      2. Rejected
                        1. Failure or Error Occurred
                          1. Reason for Rejection
                          2. State Transitions
                            1. Immutability of Settled Promises
                          3. Creating Promises
                            1. The Promise Constructor
                              1. Syntax and Usage
                                1. Executor Function
                                  1. Synchronous Execution
                                    1. Parameters: resolve and reject
                                  2. The resolve Function
                                    1. Resolving with a Value
                                      1. Resolving with Another Promise
                                        1. Thenable Objects
                                        2. The reject Function
                                          1. Rejecting with an Error
                                            1. Rejecting with Any Value
                                          2. Consuming Promises
                                            1. The then Method for Success
                                              1. Chaining Success Handlers
                                                1. Returning Values from then
                                                  1. Transformation of Values
                                                  2. The catch Method for Errors
                                                    1. Handling Rejections
                                                      1. Chaining Error Handlers
                                                        1. Error Recovery
                                                        2. The finally Method for Cleanup
                                                          1. Executing Cleanup Logic
                                                            1. Behavior with Fulfillment and Rejection
                                                              1. Value Pass-Through
                                                            2. Chaining Promises
                                                              1. Returning Values from then
                                                                1. Passing Results to Next Handler
                                                                  1. Value Transformation
                                                                  2. Returning Promises from then
                                                                    1. Flattening Nested Promises
                                                                      1. Avoiding Callback Hell in Promises
                                                                      2. Handling Multiple Asynchronous Steps
                                                                        1. Sequential Operations
                                                                          1. Data Flow Through Chain
                                                                        2. Error Handling in Promise Chains
                                                                          1. Propagating Errors
                                                                            1. Automatic Propagation Down the Chain
                                                                              1. Skipping then Handlers
                                                                              2. Centralized Error Handling with catch
                                                                                1. Catching Errors from Any Step
                                                                                  1. Error Recovery Strategies
                                                                                  2. Unhandled Promise Rejections
                                                                                    1. Detection and Warnings
                                                                                      1. Global Handlers
                                                                                        1. unhandledrejection Event
                                                                                          1. rejectionhandled Event
                                                                                      2. Static Promise Methods
                                                                                        1. Promise.all
                                                                                          1. Handling Multiple Concurrent Promises
                                                                                            1. Aggregating Results
                                                                                              1. Fail-Fast Behavior
                                                                                                1. Input Types and Validation
                                                                                                2. Promise.allSettled
                                                                                                  1. Waiting for All Promises to Settle
                                                                                                    1. Inspecting Outcomes
                                                                                                      1. Fulfilled Results
                                                                                                        1. Rejected Results
                                                                                                        2. Use Cases for Resilient Operations
                                                                                                        3. Promise.race
                                                                                                          1. Getting the First Settled Promise
                                                                                                            1. Use Cases and Limitations
                                                                                                              1. Timeout Implementations
                                                                                                              2. Promise.any
                                                                                                                1. Getting the First Fulfilled Promise
                                                                                                                  1. Handling All Rejections
                                                                                                                    1. AggregateError
                                                                                                                    2. Promise.resolve
                                                                                                                      1. Creating a Resolved Promise
                                                                                                                        1. Wrapping Non-Promise Values
                                                                                                                          1. Thenable Conversion
                                                                                                                          2. Promise.reject
                                                                                                                            1. Creating a Rejected Promise
                                                                                                                              1. Use Cases in Testing and Error Simulation

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                                                                                                                          2. Legacy Asynchronous Patterns: Callbacks

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                                                                                                                          4. Async/Await Syntax