26 lines
900 B
Markdown
26 lines
900 B
Markdown
---
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title: mask
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tags: string,intermediate
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firstSeen: 2018-01-01T13:02:59+02:00
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lastUpdated: 2020-10-21T21:54:53+03:00
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---
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Replaces all but the last `num` of characters with the specified mask character.
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- Use `String.prototype.slice()` to grab the portion of the characters that will remain unmasked.
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- Use `String.padStart()` to fill the beginning of the string with the `mask` character up to the original length.
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- If `num` is negative, the unmasked characters will be at the start of the string.
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- Omit the second argument, `num`, to keep a default of `4` characters unmasked.
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- Omit the third argument, `mask`, to use a default character of `'*'` for the mask.
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```js
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const mask = (cc, num = 4, mask = '*') =>
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`${cc}`.slice(-num).padStart(`${cc}`.length, mask);
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```
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```js
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mask(1234567890); // '******7890'
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mask(1234567890, 3); // '*******890'
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mask(1234567890, -4, '$'); // '$$$$567890'
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```
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