tsconfig.json

{
    "compilerOptions": {
        /* Basic Options */
        "target": "ES5", /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017','ES2018' or 'ESNEXT'. */
        "module": "ESNext", /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', or 'ESNext'. */
        "moduleResolution": "Node",
        "declaration": true, /* Generates corresponding '.d.ts' file. */
        "outDir": "./lib", /* Redirect output structure to the directory. */
        "rootDir": "./src", /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
        "esModuleInterop": true,

        /* Strict Type-Checking Options */
        "strict": true, /* Enable all strict type-checking options. */

        /* Additional Checks */
        "noImplicitReturns": true, /* Report error when not all code paths in function return a value. */
        "noFallthroughCasesInSwitch": true, /* Report errors for fallthrough cases in switch statement. */
        "noUncheckedIndexedAccess": true /* Turning on noUncheckedIndexedAccess will add undefined to any un-declared field in the type. */
    },
    "include": [
        "src/**/*"
    ]
}