rn-cli.config.js

'use strict';

var blacklist = require('./node_modules/react-native/packager/blacklist');

var path = require('path');

/**
 * Default configuration for the CLI.
 *
 * If you need to override any of this functions do so by defining the file
 * `rn-cli.config.js` on the root of your project with the functions you need
 * to tweak.
 */
var config = {
    getProjectRoots() {
        return getRoots();
    },

      /**
   * Specify where to look for assets that are referenced using
   * `image!<image_name>`. Asset directories for images referenced using
   * `./<image.extension>` don't require any entry in here.
   */
    getAssetRoots() {
        return getRoots();
    },

      /**
   * Returns a regular expression for modules that should be ignored by the
   * packager on a given platform.
   */
    getBlacklistRE(platform) {
        let root = this.getProjectRoots();
        let ignore_path = root + "/web/javascripts/index.js";
        return blacklist(platform, [ignore_path]);
    }
};

function getRoots() {
    if (__dirname.match(/node_modules[\/\\]react-native[\/\\]local-cli$/)) {
        // packager is running from node_modules of another project
        return [path.resolve(__dirname, '../../..')];
    } else if (__dirname.match(/Pods[\/\\]React[\/\\]packager$/)) {
        // packager is running from node_modules of another project
        return [path.resolve(__dirname, '../../..')];
    } else {
        return [path.resolve(__dirname, '..')];
    }
}


module.exports = config;

Actually what is the rn-cli.config.js and what's it for?
I just started to code with typescript, and it's a file of one of those steps to set.

@WickyLeung: nobody knows.

@br4nnigan: you can create a file named "rn-cli.config.js" and run the following script react-native start --config rn-cli.config.js