tsconfig.json

{
    "compilerOptions": {
        "watch": false,
        "noImplicitAny": true,
        "target": "es5",
        // The 'commonjs' specification is needed in order to transpile
        // proper NodeJS code. Otherwise there may be some code where
        // certain features aren't supported in Node. For more context, 
        // please look at the "Code Generation for Modules" section in 
        // 'https://www.typescriptlang.org/docs/handbook/modules.html' 
        "module": "commonjs",
        "moduleResolution": "node",
        "typeRoots": ["./node_modules/@types"],
        "lib": [
            "es2015",
            "dom"
        ],
        // Note, 'sourceMap' isn't a supported attribute in gulp, so it will be ignored
        // (aka, no-op) when this file is processed by gulp. 
        // Please see https://github.com/ivogabe/gulp-typescript for more context, which 
        // notes the issue as unsupported.
        "sourceMap": true,
        "baseUrl": "src",
        "outDir": "./lib",
        // Generate the typings (d.ts) file
        "declaration": true
    }
}