23 lines
641 B
Markdown
23 lines
641 B
Markdown
---
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title: unfold
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tags: function,array,intermediate
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---
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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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``` |