Init repo

.babelrc

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+{
+  "presets": [
+    [
+      "@babel/preset-env",
+      {
+        "targets": "> 0.25%, not dead, not op_mini >=0"
+      }
+    ],
+    "@babel/preset-typescript"
+  ]
+}

.eslintrc.js

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+module.exports = {
+  env: {
+    browser: true,
+    es6: true,
+    node: true,
+  },
+  extends: [
+    'eslint:recommended',
+    'plugin:@typescript-eslint/eslint-recommended',
+    'plugin:prettier/recommended',
+  ],
+  globals: {
+    Atomics: 'readonly',
+    SharedArrayBuffer: 'readonly',
+  },
+  parser: '@typescript-eslint/parser',
+  parserOptions: {
+    ecmaVersion: 11,
+    sourceType: 'module',
+  },
+  plugins: ['@typescript-eslint', 'prettier'],
+  rules: {
+    indent: ['error', 2],
+    'linebreak-style': ['error', 'unix'],
+    quotes: ['error', 'single'],
+    semi: ['error', 'always'],
+  },
+};

.gitignore

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+node_modules
+dist

.prettierignore

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+dist
+node_modules

.prettierrc

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+{
+  "bracketSpacing": false,
+  "singleQuote": true,
+  "printWidth": 80,
+  "trailingComma": "all"
+}

Basic32.ts

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+const SIMILAR_CHAR = {
+  O: '0',
+  I: '1',
+  L: '1',
+  B: '8',
+};
+
+const CASTABLE_CHAR = {
+  O: 'W',
+  I: 'X',
+  L: 'Y',
+  B: 'Z',
+};
+
+class Base32OTP {
+  readonly digits: number;
+  readonly outputDigits: number;
+
+  constructor(digits = 6) {
+    this.digits = digits;
+    this.outputDigits = Number(Math.pow(10, digits) - 1).toString(32).length;
+  }
+
+  encode(rawCode: number | string) {
+    if (
+      typeof rawCode === 'string' &&
+      (!/^\d+$/.test(rawCode) || rawCode.length > this.digits)
+    )
+      throw new Error('Invalid code passed');
+
+    let code = Number(rawCode).toString(32).toUpperCase();
+
+    Object.keys(CASTABLE_CHAR).forEach(function (badLetter) {
+      code = code.replace(
+        new RegExp(badLetter, 'g'),
+
+        CASTABLE_CHAR[<keyof typeof CASTABLE_CHAR>badLetter],
+      );
+    });
+
+    const template = Array.from({length: this.outputDigits}, function () {
+      return '0';
+    });
+
+    return Object.assign(template, code.split('').reverse()).reverse().join('');
+  }
+
+  decode(rawCode: string) {
+    if (
+      /^\d+$/.test(rawCode) &&
+      rawCode.length === this.digits &&
+      rawCode.length !== this.outputDigits
+    )
+      return rawCode;
+
+    if (!/^[\dA-Za-z]+$/.test(rawCode) || rawCode.length !== this.outputDigits)
+      throw new Error(
+        'Code should be ' + this.outputDigits + ' alphanumeric characters',
+      );
+
+    let code = rawCode.toUpperCase();
+
+    Object.keys(SIMILAR_CHAR).forEach(function (badLetter) {
+      code = code.replace(
+        new RegExp(badLetter, 'g'),
+
+        SIMILAR_CHAR[<keyof typeof SIMILAR_CHAR>badLetter],
+      );
+    });
+
+    Object.keys(CASTABLE_CHAR).forEach(function (badLetter) {
+      code = code.replace(
+        new RegExp(CASTABLE_CHAR[<keyof typeof CASTABLE_CHAR>badLetter], 'g'),
+
+        badLetter,
+      );
+    });
+
+    const template = Array.from({length: this.digits}, () => '0');
+
+    code = parseInt(code, 32).toString(10);
+
+    return Object.assign(template, code.split('').reverse()).reverse().join('');
+  }
+}
+
+export default Base32OTP;

LICENSE

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+Copyright (c) 2020 Russell Steadman
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+# Basic32
+
+Basic32 encodes and decodes OTP (One-time passcode) tokens to and from a standard length Base32 string, effectively making them shorter.
+
+## Why?
+
+Basic32 decreases the number of characters needed for a OTP code, making the code easier for users to remember.
+
+| Regular TOTP | Encoded TOTP |
+| ------------ | ------------ |
+| 6 digits     | 4 chars      |
+| 7 digits     | 5 chars      |
+| 8 digits     | 6 chars      |
+| 9 digits     | 6 chars      |
+
+## Installation
+
+```sh
+npm i basic32
+```
+
+```javascript
+import Basic32 from 'basic32';
+```
+
+## Usage
+
+```javascript
+import Basic32 from 'basic32';
+
+/* Initialize the encoder */
+const basic = new Basic32(/* Number of digits in OTP code, default: 6 */);
+
+/* Encode a number or string */
+basic.encode(123456); // -> "3WX0"
+basic.encode('123456'); // -> "3WX0"
+
+/* Decode a string */
+basic.decode('3WX0'); // -> "123456"
+
+/* Decode a string, but zero is switched with letter o */
+basic.decode('3WXO'); // -> "123456"
+
+/* Decode the wrong number of characters */
+basic.decode('3WX0A'); // -> new Error("Code should be 4 alphanumeric characters")
+
+/* Decode an already decoded string */
+basic.decode('123456'); // -> "123456"
+```
+
+## Character Corrections
+
+The following character transposition errors are automatically fixed.
+
+| User Writes | Interpreted |
+| ----------- | ----------- |
+| (Letter) O  | (Number) 0  |
+| (Letter) I  | (Number) 1  |
+| (Letter) L  | (Number) 1  |
+| (Letter) B  | (Number) 8  |
+
+## License
+
+MIT © 2020 [Russell Steadman](https://github.com/teamtofu). See LICENSE.