tsconfig-tools.json

{
  "compilerOptions": {
    /* Basic Options */
    "target": "es5",                          /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', or 'ESNEXT'. */
    "lib": ["es6", "dom"],                    /* Specify library files to be included in the compilation:  */
    "strict": true,                           /* Enable all strict type-checking options. */
    "downlevelIteration": true,               /* Provide full support for iterables in 'for-of', spread, and destructuring when targeting 'ES5' or 'ES3'. */
  }
}