JavaScript Generator Functions

A Generator Function in JavaScript is a special type of function that can pause its execution and resume later. It is defined using the function* syntax and uses the yield keyword to pause execution.

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What Is a Generator?

A generator function:

• Does not run to completion immediately
• Returns a generator object when called
• Can pause at each yield statement
• Can be resumed using the .next() method

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Syntax

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Example 1: Simple Generator

Each call to .next() resumes execution until the next yield.

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Example 2: Generator with Loop

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Example 3: Passing Data to yield

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Generator Methods

Generators support .next(), .return(), and .throw() methods for controlling execution.

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Example 4: Generator with return() and throw()

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Use Cases of Generators

• Lazy iteration (e.g., reading large data step-by-step)
• Creating custom iterable data structures
• Asynchronous control flow management
• State machines
• Pausable computations like animations or games

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Key Takeaways

• Declared with function* and use yield to pause execution.
• Calling a generator returns an iterator with .next(), .return(), and .throw().
• Useful for custom iteration, async programming, and complex control flow.
• Can be iterated using for...of loops over yielded values.