refactor: Migrate to TypeScript

Author: mrodrig

.eslintrc

@@ -0,0 +1,52 @@
+module.exports = {
+    root: true,
+    env: {
+        es2022: true,
+        node: true,
+        mocha: true,
+    },
+    parserOptions: {
+        ecmaVersion: 13,
+        project: ['tsconfig.json', 'tsconfig.dev.json'],
+        sourceType: 'module',
+        tsconfigRootDir: __dirname,
+    },
+    extends: [
+        'eslint:recommended',
+        'plugin:import/errors',
+        'plugin:import/warnings',
+        'plugin:import/typescript',
+        'plugin:@typescript-eslint/recommended',
+    ],
+    parser: '@typescript-eslint/parser',
+    ignorePatterns: [
+        '/lib/**/*', // Ignore built files.
+    ],
+    plugins: [
+        '@typescript-eslint',
+        'import',
+    ],
+    rules: {
+        // Basic ES6
+        indent: [
+            'error', 4, { // use 4 spaces for indents
+                'SwitchCase': 1, // indent case within switch
+            }
+        ],
+        'linebreak-style': 0, // mixed environment let git config enforce line endings
+        quotes: ['error', 'single'],
+        semi: ['error', 'always'],
+        'no-var': 'error',
+        'no-console': 0, // allow use of console.log,
+        'arrow-body-style': [0, 'always'],
+        'max-len': 0,
+        'camelcase': 1,
+        'import/no-unresolved': [
+            'error', {
+                // https://github.com/firebase/firebase-admin-node/discussions/1359
+                ignore: ['^firebase-admin/.+'],
+            },
+        ],
+        '@typescript-eslint/consistent-type-definitions': 'warn'
+    },
+};

.eslintrc.js

@@ -10,3 +10,6 @@ node_modules
 
 # Debug logs
 npm-debug.log
+
+# Built JavaScript files
+lib

.gitignore

@@ -1,12 +1,26 @@
-test/
-.git*
+# Debug Logs
 npm-debug.log
-.travis.yml
-.eslintrc
-node_modules
-coverage
+
+# Uncompiled Source Files
+src
+
+# Node Modules
+node_modules/
+node_modules/*
+
+# Configuration Files
+.eslintrc*
+tsconfig*
+
+# Test/Coverage Files
+coverage/
+coverage/*
+.nycrc
 .nyc_output
-upgrade_guides
-tslint.json
-_config.yml
+.nyc_output/*
 .coveralls.yml
+lib/test
+
+# Github Configuration Files
+_config.yml
+.git*

.npmignore

@@ -0,0 +1,16 @@
+{
+    "check-coverage": true,
+    "all": true,
+    "include": [
+        "src/**/!(*.test.*).[tj]s?(x)"
+    ],
+    "exclude": [
+        "test/**/*.*"
+    ],
+    "reporter": [
+        "lcov",
+        "text-summary",
+        "text"
+    ],
+    "report-dir": "coverage"
+}

.nycrc

@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2014-2020 Michael Rodrigues
+Copyright (c) 2014-Present Michael Rodrigues
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal