title: eCharts import does not work. Fails with _DEV__ is not defined
body: <p>I installed using NPM, echarts library in this way</p>
  
  <pre><code>npm install echarts --save
  </code></pre>
  
  <p>Following the <a href="http://echarts.baidu.com/tutorial.html#%E8%87%AA%E5%AE%9A%E4%B9%89%E6%9E%84%E5%BB%BA%20ECharts" rel="nofollow noreferrer">documentation</a> I wrote in my code</p>
  
  <p><code>import * as echarts from 'echarts'</code></p>
  
  <p>then I tried a very simple example</p>
  
  <pre><code>const $chart = $('#chart')
  let myChart = echarts.init($chart)
  const option = {
    title: {
      text: 'ECharts entry example'
    },
    tooltip: {},
    legend: {
      data: ['Sales']
    },
    xAxis: {
      data: ['shirt', 'cardign', 'chiffon shirt', 'pants', 'heels', 'socks']
    },
    yAxis: {},
    series: [
      {
        name: 'Sales',
        type: 'bar',
        data: [5, 20, 36, 10, 10, 20]
      }
    ]
  }
  myChart.setOption(option)
  </code></pre>
  
  <p>but I got this error </p>
  
  <pre><code>ReferenceError: __DEV__ is not defined
  </code></pre>
  
  <p>What do you think is the problem? I can't find documentation about this error...</p>