# Custom Component

From base library 1.6.3 and later, Mini Programs support concise componential programming. The base library 1.6.3 or higher is required for all custom component related features.

Developers can abstract feature modules in a page into custom components to reuse them in different pages, or split a page into multiple low-coupling modules for easy code maintenance. Custom components are used in almost the same way as base components.

# Creating Custom Component

Similar to a page, a custom component consists of json, wxml, wxss, and js files. To write a custom component, you first need to make a custom component declaration in the json file (set the files as custom components by setting the component field to true):

  "component": true

In the meanwhile, write a component template in the wxml file and a component style in the wxss file in a same way that you write a page. For details and considerations, see Component Template and Style.

Code example:

<!-- This is the internal WXML structure of the custom component -->
<view class="inner">
/*  This style only applies to this custom component  */
.inner {
  color: red;

Note: ID selectors, attribute selectors, and tag name selectors should not be used in the component's wxss.

In the custom component's js file, you need to register the component using Component() and provide the component's property definitions, internal data, and custom methods.

The property values and internal data of the component are used to render the component's wxml. The property values are passed in from outside the component. For details, see Component Constructor.

Code example:

  properties: {
    // The innerText property is defined here, and the property value can be specified when the component is used.
    innerText: {
      type: String,
      value: 'default value',
  data: {
    // Here are some component internal data
    someData: {}
  methods: {
    // Here is a custom method
    customMethod: function(){}

# Using Custom Component

Before using a registered custom component, make a reference declaration in the json file of the page. You need to provide the tag name of each custom component and the file path of the corresponding custom component:

  "usingComponents": {
    "component-tag-name": "path/to/the/custom/component"

As such, you can use custom components like you would with base components in the wxml of the page. The node name is the tag name of the custom component, and the node property is the property value passed to the component.

As of Weixin DevTools 1.02.1810190, the usingComponents field can be declared in app.json. The custom component declared here is considered as a global custom component, which can be used directly in pages or custom components within Mini Programs without the need to declare it again.

Code example:

Preview with Developer Tool

  <!-- The following is a reference to a custom component -->
  <component-tag-name inner-text="Some text"></component-tag-name>

The custom component's wxml node structure, after being combined with the data, will be inserted into the reference location.

# Notes

Please note the following:

  • Since the tag name of a WXML node can only be a combination of lowercase letters, hyphens (-), and underscores (_), the tag name of a custom component can contain these characters only.
  • Custom components can also reference other custom components in a similar way to referencing custom components by pages (the usingComponents field is used).
  • The name of the project's root directory where the custom components and pages are located cannot be prefixed with "wx-". Otherwise, an error will occur.

Note that using usingComponents in the page file will make the prototype of the page's this object slightly different, including:

  • The prototype that uses the usingComponents page differs from the prototype that does not use usingComponents, i.e. the result of Object.getPrototypeOf(this) is different.
  • More methods, such selectComponent, are available when usingComponents is used.
  • For performance reasons, when usingComponents is used, the content of setData is not deep copied directly, that is, this.data.field === obj after this.setData({ field: obj }) is called. (Deep copy occurs when this value is passed between components.)

For complicated pages, retest is required if the usingComponents definition field is added or removed.