之前初始化都没问题的，有一次初始化发现报错说网络有问题，然后再初始化就报下面的错误:

This will walk you through creating a new React Native project in /Users/dengjiewen/Desktop/joke
Using yarn v0.20.3
Installing react-native...
yarn add v0.20.3
info No lockfile found.
[1/4] 🔍  Resolving packages...
error An unexpected error occurred: "https://registry.yarnpkg.com/react-native: read ETIMEDOUT".
info If you think this is a bug, please open a bug report with the information provided in "/Users/dengjiewen/Desktop/joke/yarn-error.log".
info Visit https://yarnpkg.com/en/docs/cli/add for documentation about this command.
{ Error: Command failed: yarn add react-native --exact
    at checkExecSyncError (child_process.js:490:13)
    at execSync (child_process.js:530:13)
    at run (/usr/local/lib/node_modules/react-native-cli/index.js:294:5)
    at createProject (/usr/local/lib/node_modules/react-native-cli/index.js:249:3)
    at init (/usr/local/lib/node_modules/react-native-cli/index.js:200:5)
    at Object.<anonymous> (/usr/local/lib/node_modules/react-native-cli/index.js:153:7)
    at Module._compile (module.js:571:32)
    at Object.Module._extensions..js (module.js:580:10)
    at Module.load (module.js:488:32)
    at tryModuleLoad (module.js:447:12)
  error: null,
  cmd: 'yarn add react-native --exact',
  file: '/bin/sh',
  args: [ '/bin/sh', '-c', 'yarn add react-native --exact' ],
  options: 
   { stdio: [ [Object], [Object], [Object] ],
     shell: true,
     file: '/bin/sh',
     args: [ '/bin/sh', '-c', 'yarn add react-native --exact' ],
     envPairs: 
      [ 'TERM_PROGRAM=Apple_Terminal',
        'ANDROID_HOME=/Users/dengjiewen/Library/Android/sdk',
        'SHELL=/bin/bash',
        'TERM=xterm-256color',
        'TMPDIR=/var/folders/t4/k953mqjj7b71xjmdr0bx_nz40000gn/T/',
        'Apple_PubSub_Socket_Render=/private/tmp/com.apple.launchd.jeiwp8RAEI/Render',
        'TERM_PROGRAM_VERSION=377',
        'OLDPWD=/Users/dengjiewen',
        'TERM_SESSION_ID=BED38688-46DE-42D7-AC7B-D522572F3D5A',
        'USER=dengjiewen',
        'SSH_AUTH_SOCK=/private/tmp/com.apple.launchd.AMMxRnfsSb/Listeners',
        '__CF_USER_TEXT_ENCODING=0x1F5:0x19:0x34',
        'PATH=/Library/Java/JavaVirtualMachines/jdk1.8.0_121-b13.jdk/Contents/Home/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:.:/Users/dengjiewen/Library/Android/sdk/tools:/Users/dengjiewen/Library/Android/sdk/platform-tools',
        'PWD=/Users/dengjiewen/Desktop',
        'JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home',
        'LANG=zh_CN.UTF-8',
        'XPC_FLAGS=0x0',
        'XPC_SERVICE_NAME=0',
        'SHLVL=1',
        'HOME=/Users/dengjiewen',
        'LOGNAME=dengjiewen',
        'CLASSPATH=JAVA_HOME/lib/tools.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_121-b13.jdk/Contents/Home/lib/dt.jar:.',
        '_=/usr/local/bin/react-native' ] },
  envPairs: 
   [ 'TERM_PROGRAM=Apple_Terminal',
     'ANDROID_HOME=/Users/dengjiewen/Library/Android/sdk',
     'SHELL=/bin/bash',
     'TERM=xterm-256color',
     'TMPDIR=/var/folders/t4/k953mqjj7b71xjmdr0bx_nz40000gn/T/',
     'Apple_PubSub_Socket_Render=/private/tmp/com.apple.launchd.jeiwp8RAEI/Render',
     'TERM_PROGRAM_VERSION=377',
     'OLDPWD=/Users/dengjiewen',
     'TERM_SESSION_ID=BED38688-46DE-42D7-AC7B-D522572F3D5A',
     'USER=dengjiewen',
     'SSH_AUTH_SOCK=/private/tmp/com.apple.launchd.AMMxRnfsSb/Listeners',
     '__CF_USER_TEXT_ENCODING=0x1F5:0x19:0x34',
     'PATH=/Library/Java/JavaVirtualMachines/jdk1.8.0_121-b13.jdk/Contents/Home/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:.:/Users/dengjiewen/Library/Android/sdk/tools:/Users/dengjiewen/Library/Android/sdk/platform-tools',
     'PWD=/Users/dengjiewen/Desktop',
     'JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home',
     'LANG=zh_CN.UTF-8',
     'XPC_FLAGS=0x0',
     'XPC_SERVICE_NAME=0',
     'SHLVL=1',
     'HOME=/Users/dengjiewen',
     'LOGNAME=dengjiewen',
     'CLASSPATH=JAVA_HOME/lib/tools.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_121-b13.jdk/Contents/Home/lib/dt.jar:.',
     '_=/usr/local/bin/react-native' ],
  stderr: null,
  stdout: null,
  pid: 495,
  output: [ null, null, null ],
  signal: null,
  status: 1 }
Command `yarn add react-native --exact` failed.

出现这个问题，可以试一下执行下面二行代码

npm config set registry https://registry.npm.taobao.org
npm config set disturl https://npm.taobao.org/dist

然后再执行一下初始化就可以了。