25 lines
628 B
Markdown
25 lines
628 B
Markdown
---
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title: Left substring generator
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tags: string,generator
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cover: boutique-home-office-1
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author: chalarangelo
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firstSeen: 2022-07-24T05:00:00-04:00
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---
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Generates all left substrings of a given string.
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- Use `String.prototype.length` to terminate early if the string is empty.
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- Use a `for...in` loop and `String.prototype.slice()` to `yield` each substring of the given string, starting at the beginning.
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```js
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const leftSubstrGenerator = function* (str) {
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if (!str.length) return;
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for (let i in str) yield str.slice(0, i + 1);
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};
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```
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```js
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[...leftSubstrGenerator('hello')];
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// [ 'h', 'he', 'hel', 'hell', 'hello' ]
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```
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