C:\MyApp\node-v10.16.3-win-x64\node_modules\react-native-cli
这个index.js里有很多有用的信息，当遇到react native的各种错误时，搞清楚他们的原理有助于问题定位：
'use strict'; var fs = require('fs'); var path = require('path'); var exec = require('child_process').exec; var execSync = require('child_process').execSync; var chalk = require('chalk'); var prompt = require('prompt'); var semver = require('semver'); // Use Yarn if available, it's much faster than the npm client. // Return the version of yarn installed on the system, null if yarn is not available. function getYarnVersionIfAvailable() {
