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Implement a Range Class Using the Iterator Protocol Manually (No Generator Functions Allowed)

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The problem

Problem, as an interviewer would state it: "Implement a Range class that can be used in for...of, spread and destructuring, by implementing the iterator protocol by hand. No generator functions."

Examples:

Code
[...new Range(0, 10, 3)];               // [0, 3, 6, 9]
for (const x of new Range(5, 0, -2)) {} // 5, 3, 1

Clarifying questions expected:

  • Is the end exclusive, and are negative steps supported?
  • Should a range be iterable more than once, and should it support an infinite end?
  • What should happen for a step of zero, and what about fractional steps?

Code / implementation expected: Yes — real, direct proof the object works with every consumer of the iterable protocol, including early exit.

  • js-coding
  • utility
  • algorithm

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6 min read · 9 sections

Run the code

Edit the code and run it here. Each console line with an expected value becomes a test.

JavaScriptReal, direct proof: a hand-written iterator Range works with every consumer, supports an infinite end, avoids float drift, and reports exactly when return() is called
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