Ushio-cn-old/yimian/iot/mqtt/smartfarm/node_modules/nanoid

Nano ID

A tiny, secure URL-friendly unique string ID generator for JavaScript.

var nanoid = require('nanoid')
model.id = nanoid() //=> "Uakgb_J5m9g~0JDMbcJqLJ"

Safe. It uses cryptographically strong random APIs and guarantees a proper distribution of symbols.

Small. Only 179 bytes (minified and gzipped). No dependencies. It uses Size Limit to control size.

Compact. It uses more symbols than UUID (A-Za-z0-9_~) and has the same number of unique options in just 22 symbols instead of 36.

The generator supports Node.js and all browsers starting from IE 11.

Security

See a good article about random generators theory: Secure random values (in Node.js)

Unpredictability

Instead of unsafe Math.random() Nano ID uses crypto module in Node.js and Web Crypto API in browsers.

Uniformity

random % alphabet is a popular mistake to make when coding an ID generator. The spread will not be even; there will be a lower chance for some symbols to appear compared to others—so it will reduce the number of tries when brute-forcing.

Nano ID uses a better algorithm and tests uniformity:

Comparison with UUID

Nano ID is similar to UUID v4 (random-based). It uses the same number of random bits in ID, so it has the same collision probability:

For there to be a one in a billion chance of duplication, 103 trillion version 4 IDs must be generated.

There are only 2 differences between Nano ID and UUID v4:

1. Nano ID uses a bigger alphabet for ID, so the same random bits are packed in just 22 symbols instead of 36.
2. Nano ID code is 2 times smaller in size than uuid/v4 package: 179 bytes instead of 435.

Benchmark

$ ./benchmark
nanoid          375,840 ops/sec
nanoid/generate 268,747 ops/sec
uuid/v4         374,767 ops/sec
shortid          41,260 ops/sec

Usage

Normal

The main module uses URL-friendly symbols (A-Za-z0-9_~) and returns an ID with 22 characters (to have the same collisions probability as UUID v4).

var nanoid = require('nanoid')
model.id = nanoid() //=> "Uakgb_J5m9g~0JDMbcJqLJ"

Symbols -,.() are not encoded in URL, but in the end of a link they could be identified as a punctuation symbol.

If you want to reduce ID length (and increase collisions probability), you can pass length as argument:

nanoid(10) //=> "IRFa~VaY2b"

Custom Alphabet or Length

If you want to change the ID alphabet or the length you can use low-level generate module.

var generate = require('nanoid/generate')
model.id = generate('1234567890abcdef', 10) //=> "4f90d13a42"

Alphabet must contain less than 256 symbols.

Custom Random Bytes Generator

You can replace the default safe random generator using the format module. For instance, to use seed-based generator.

var format = require('nanoid/format')

function random (size) {
  var result = []
  for (var i = 0; i < size; i++) result.push(randomByte())
  return result
}

format(random, "abcdef", 10) //=> "fbaefaadeb"

random callback must accept the array size and return an array with random numbers.

If you want to use the same URL-friendly symbols with format, you can get default alphabet from the url module:

var url = require('nanoid/url')
format(random, url, 10) //=> "93ce_Ltuub"

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