运行nodejs项目，npm start启动项目import报错，SyntaxError: Cannot use import statement outside a module

$ npm start                                                                                                                                                                  
                                                                                                                                                                             
> m-mall-admin@1.0.0 start D:\SoftwareAndProgram\program\weixin\miniprogram\mini-mall\mini-mall-admin                                                                        
> babel-node ./bin/www                                                                                                                                                       
                                                                                                                                                                             
(node:4488) Warning: To load an ES module, set "type": "module" in the package.json or use the .mjs extension.                                                               
D:\SoftwareAndProgram\program\weixin\miniprogram\mini-mall\mini-mall-admin\bin\www:4                                                                                         
import app from '../app';                                                                                                                                                    
^^^^^^                                                                                                                                                                       
                                                                                                                                                                             
SyntaxError: Cannot use import statement outside a module                                                                                                                    
    at wrapSafe (internal/modules/cjs/loader.js:1043:16)                                                                                                                     
    at Module._compile (internal/modules/cjs/loader.js:1091:27)                                                                                                              
    at loader (D:\SoftwareAndProgram\program\weixin\miniprogram\mini-mall\mini-mall-admin\node_modules\babel-register\lib\node.js:146:5)                                     
    at Object.require.extensions.<computed> [as .js] (D:\SoftwareAndProgram\program\weixin\miniprogram\mini-mall\mini-mall-admin\node_modules\babel-register\lib\node.js:156:
7)                                                                                                                                                                           
    at Module.load (internal/modules/cjs/loader.js:976:32)                                                                                                                   
    at Function.Module._load (internal/modules/cjs/loader.js:884:14)                                                                                                         
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:67:12)                                                                                      
    at D:\SoftwareAndProgram\program\weixin\miniprogram\mini-mall\mini-mall-admin\node_modules\babel-cli\lib\_babel-node.js:151:24                                           
    at Object.<anonymous> (D:\SoftwareAndProgram\program\weixin\miniprogram\mini-mall\mini-mall-admin\node_modules\babel-cli\lib\_babel-node.js:152:7)                       
    at Module._compile (internal/modules/cjs/loader.js:1121:30)                                                                                                              
npm ERR! code ELIFECYCLE                                                                                                                                                     
npm ERR! errno 1                                                                                                                                                             
npm ERR! m-mall-admin@1.0.0 start: `babel-node ./bin/www`                                                                                                                    
npm ERR! Exit status 1                                                                                                                                                       
npm ERR!                                                                                                                                                                     
npm ERR! Failed at the m-mall-admin@1.0.0 start script.                                                                                                                      
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.                                                                           
                                                                                                                                                                             
npm ERR! A complete log of this run can be found in:                                                                                                                         
npm ERR!     C:\Users\lenovo\AppData\Roaming\npm-cache\_logs\2019-11-29T03_31_13_816Z-debug.log                                                                              
                                                                                                                                                                             
D:\SoftwareAndProgram\program\weixin\miniprogram\mini-mall\mini-mall-admin (master -> origin) (m-mall-admin@1.0.0)                                                           
$ node -v                                                                                                                                                                    
v13.2.0                                                                                                                                                                      
                                                                                                                                                                             
D:\SoftwareAndProgram\program\weixin\miniprogram\mini-mall\mini-mall-admin (master -> origin) (m-mall-admin@1.0.0)                                                           
$ npm -v                                                                                                                                                                     
6.13.1                                                                                                                                                                       
                                                                                                                                                                             　　

大概意思是nodejs不支持import语法，如果要支持，需要babel来支持。

babel的安装
所以我们来安装babel吧， 有了babel， 能够使用更多高级词法！

在项目根目录下，执行：

npm install --save babel-core
npm install --save babel-preset-env 或者 npm install --save babel-preset-es2015
npm install babel-cli -g

接着在项目根目录下创建一个名字为.babelrc的文件， 文件内容入如下（ 要注意window系统下创建这种文件系统会提示你：“必须键入文件名” ， 你可以找别的方式去创建， 我是在开发工具的工程目录中把这个文件创建出来的，也可以用cmder神器的vim命令）：

 {
    "presets": [
      "es2015"
    ],
    "plugins": []
}

或者：

{                
    "presets": [ 
         "env"   
     ],          
    "plugins": []
}                

到目前为止babel算是安装完毕了。

接下来可以用npm start和babel-node app.js运行项目。

　　

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