1 | // This file replaces `async/index.js` in bundlers like webpack or Rollup,
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2 | // according to `browser` config in `package.json`.
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3 |
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4 | var crypto = self.crypto || self.msCrypto
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5 |
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6 | // This alphabet uses a-z A-Z 0-9 _- symbols.
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7 | // Symbols are generated for smaller size.
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8 | // -_zyxwvutsrqponmlkjihgfedcba9876543210ZYXWVUTSRQPONMLKJIHGFEDCBA
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9 | var url = '-_'
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10 | // Loop from 36 to 0 (from z to a and 9 to 0 in Base36).
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11 | var i = 36
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12 | while (i--) {
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13 | // 36 is radix. Number.prototype.toString(36) returns number
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14 | // in Base36 representation. Base36 is like hex, but it uses 0–9 and a-z.
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15 | url += i.toString(36)
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16 | }
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17 | // Loop from 36 to 10 (from Z to A in Base36).
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18 | i = 36
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19 | while (i-- - 10) {
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20 | url += i.toString(36).toUpperCase()
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21 | }
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22 |
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23 | module.exports = function (size) {
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24 | var id = ''
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25 | var bytes = crypto.getRandomValues(new Uint8Array(size || 21))
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26 | i = size || 21
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27 |
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28 | // Compact alternative for `for (var i = 0; i < size; i++)`
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29 | while (i--) {
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30 | // We can’t use bytes bigger than the alphabet. 63 is 00111111 bitmask.
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31 | // This mask reduces random byte 0-255 to 0-63 values.
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32 | // There is no need in `|| ''` and `* 1.6` hacks in here,
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33 | // because bitmask trim bytes exact to alphabet size.
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34 | id += url[bytes[i] & 63]
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35 | }
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36 | return Promise.resolve(id)
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37 | }
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