8ee50178f3
Correct: `Array.from()` (it’s a static method) Incorrect: `Array.join()` (doesn’t exist; it’s a prototype method) This patch uses the common `#` syntax to denote `.prototype.`.
21 lines
597 B
Markdown
21 lines
597 B
Markdown
### unfold
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Builds an array, using an iterator function and an initial seed value.
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Use a `while` loop and `Array.prototype.push()` to call the function repeatedly until it returns `false`.
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The iterator function accepts one argument (`seed`) and must always return an array with two elements ([`value`, `nextSeed`]) or `false` to terminate.
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```js
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const unfold = (fn, seed) => {
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let result = [],
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val = [null, seed];
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while ((val = fn(val[1]))) result.push(val[0]);
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return result;
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};
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```
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```js
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var f = n => (n > 50 ? false : [-n, n + 10]);
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unfold(f, 10); // [-10, -20, -30, -40, -50]
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```
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