tsconfig.json

{
    "compilerOptions": {
        "target": "es5",
        "module": "es6",
        "lib": [
            "es2015",
            "dom"
        ],
        "declaration": true, /* Generates corresponding '.d.ts' file. */
        "sourceMap": true, /* Generates corresponding '.map' file. */
        "outDir": "./lib", /* Redirect output structure to the directory. */
        "importHelpers": true, /* Import emit helpers from 'tslib'. */
        /* Strict Type-Checking Options */
        "strict": true, /* Enable all strict type-checking options. */
        "noImplicitAny": false, /* Raise error on expressions and declarations with an implied 'any' type. */
        "strictNullChecks": false, /* Enable strict null checks. */
        "moduleResolution": "node", /* Specify module resolution strategy: 'node' (Node.js) or 'classic' (TypeScript pre-1.6). */
        "types": [
            "mocha",
            "chai"
        ]
    },
    "include": [
        "./src/index-node.ts",
        "./src/index-browser.ts"
    ],
    "compileOnSave": true
}