---

title: FAQ type: wiki group: FAQ order: 8 version: 2.1

Where are legacy docs?

• Guide
• References
• Advanced
• Tools

Command errors in MS Windows

Please install Git for Windows first, see For Windows for more information.

Gradle errors in Android Studio

Downloading license-gradle-plugin.jar may trigger errors, like Connection reset or peer not authenticated. Maybe a network problem, try a proxy or VPN.

Use local image

Weex‘s native runtime support load image file from device’s disk, all you have to do set the file url like file:///sdcard/image_new0.png. As to load image file in your project, Weex is not support yet.

Error（The header content contains invalid characters) in windows

This‘s is caused by weex-toolkit’s dependency ‘http-server’, whose old version is not working well in chinese windows environment. We have fixed that, you should upgrade weex-toolkit before use that.

Playground app display nothing (white screen) after scan

Best way to find out what's happening is read debug log, you can follow this document to firgure out how to do that.

About ECMAScript Version

Weex uses JSCore in iOS and uses v8 in Android. So they both support ECMAScript 5 spec. Additionally, we do some polyfills in native environment:

• Promise in iOS/Android
• Timer APIs (setTimeout / clearTimeout / setInterval / clearInterval) in iOS/Android
• console in iOS/Android

In Browser we contains a polyfill of Promise temporarily. In the future developers can choose whether to import a polyfill by configurations.

You can also write ES6 syntax by babel with webpack. The loader will convert ES6 syntax into ES5 automatically.

If you want more ES6 polyfills you can import them into the JS Bundle as you like.

Dependencies in frontend

In Weex you may have some ways to import/require a component or a JS module. Take ES5 syntax for example:

• require('xxx.js'): depends on a JS file
• require('npm-module-name'): depends on a NPM module
• require('xxx.we'): include a we file to register a Weex custom component
• require('@weex-module/xxx'): depends on a Weex native module. Notice that it is supported only in *.we file not *.js file. If you want to use Weex native module in a *.js file, temporarily you may write like this:

// use this piece of code below to get Weex native module "modal"
var modal
__weex_define__('@weex-temp/x', function (__weex_require__) {
  modal = __weex_require__('@weex-module/modal')
})

// use APIs in "modal" module
modal.toast({message: 'hello'})

We will bring a better syntax design in the future.

iOS text line-height style is abnormal

line-height style in text component is different from h5 and Android, text value will be placed at bottom of line box because of iOS native api. We are trying to optimize it.

Android only support overflow:hidden

The overflow style in android is hidden and cannot be changed. This is the result of Android View framework. This only happens on Android, iOS will work as expected.

How to get rid of 750 adaption and calculate width/height in real pixels？

The deviceHeight and deviceWidth got in this.$getConfig() is the real device width/height in pixels, not the ones with 750-adapted.

So you can use them to calculate width/height in real pixels.

Suppose you need to display a navigation bar of fixed 88 pixels, the bar's height will be:

var height = 88 * 750 / env.deviceWidth

How to detect an native module/component supported in JavaScript?

Detect native module

var xxx = require('@weex-module/xxx')
if (xxx) {
  // todo: use this module
}
else {
  // todo: handle the exception
}

Detect native component

<template>
  <component is="{{type}}"></component>
</template>

<script>
  var type = 'xxx'
  var xxx = require('@weex-component/xxx')
  if (!xxx) {
    type = 'div' // downgrade to <div>
  }
  module.exports = {
    data: function () {
      return {
        type: type
      }
    }
  }
</script>

How to transfer data between pages

If you have 2 pages, A and B.

0. A -> B, use storage module to transfer data
1. B -> A, use storage module to transfer data

How to use repeat in Parent-Child components

If you want, You can make a repeat operation between Parent-Child components. But you must be strictly in accordance with the document syntax to write code. If there is no child component defined data, or there is no specify props that need to be passed down. It will lead to the page does not render properly.

A correct example:

<element name="child">
  <template>
    <div>
      <text style="font-size:100">{{title}}</text>
    </div>
  </template>

  <script>
    module.exports = {
      data: {
        title: null
      }
    }
  </script>
</element>
<template>
  <div>
    <child repeat="item in lists" title="{{ item.title }}"></child>
  </div>
</template>
<script>
  module.exports = {
    data: {
      lists: [
        { title: 'A' },
        { title: 'B' },
        { title: 'C' }
      ]
    },
    ready: function () {
      this.lists.splice(0, 1)
    }
  }
</script>

A wrong example：

<element name="child">
  <template>
    <div>
      <text style="font-size:100">{{title}}</text>
    </div>
  </template>
</element>
<template>
  <div>
    <child repeat="item in lists"></child>
  </div>
</template>
<script>
  module.exports = {
    data: {
      lists: [
        { title: 'A' },
        { title: 'B' },
        { title: 'C' }
      ]
    },
    ready: function () {
      this.lists.splice(0, 1)
    }
  }
</script>