ELRIWebSystem/Learning/vue/webpack/docs/env.md

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# Environment Variables
Sometimes it is practical to have different config values according to the environment that the application is running in.
As an example:
```js
// config/prod.env.js
module.exports = {
NODE_ENV: '"production"',
DEBUG_MODE: false,
API_KEY: '"..."' // this is shared between all environments
}
// config/dev.env.js
module.exports = merge(prodEnv, {
NODE_ENV: '"development"',
DEBUG_MODE: true // this overrides the DEBUG_MODE value of prod.env
})
// config/test.env.js
module.exports = merge(devEnv, {
NODE_ENV: '"testing"'
})
```
> **Note:** string variables need to be wrapped into single and double quotes `'"..."'`
So, the environment variables are:
- Production
- NODE_ENV = 'production',
- DEBUG_MODE = false,
- API_KEY = '...'
- Development
- NODE_ENV = 'development',
- DEBUG_MODE = true,
- API_KEY = '...'
- Testing
- NODE_ENV = 'testing',
- DEBUG_MODE = true,
- API_KEY = '...'
As we can see, `test.env` inherits the `dev.env` and the `dev.env` inherits the `prod.env`.
### Usage
It is simple to use the environment variables in your code. For example:
```js
Vue.config.productionTip = process.env.NODE_ENV === 'production'
```