# Data Binding

The dynamic data in WXML comes from the data of the corresponding Page.

# Simple Binding

Data binding uses the Mustache syntax (double curly brackets) to wrap the variables. It can be used for the following:

# Content

<view> {{ message }} </view>

Page({
  data: {
    message: 'Hello MINA!'
  }
})

# Component Properties (must be enclosed in double quotes)

<view id="item-{{id}}"> </view>

Page({
  data: {
    id: 0
  }
})

# Control Properties (must be enclosed in double quotes)

<view wx:if="{{condition}}"> </view>

Page({
  data: {
    condition: true
  }
})

# Keywords (must be enclosed in double quotes)

True: Boolean-type true.

false: Boolean-type false.

<checkbox checked="{{false}}"> </checkbox>

Note: Do not directly write checked="false". Its computing result is a string which represents a true value when converted to a Boolean value.

# Operations

You can implement simple operations in {{}}. This syntax supports the following methods:

# Ternary Operations

<view hidden="{{flag ? true : false}}"> Hidden </view>

# Arithmetic Operations

<view> {{a + b}} + {{c}} + d </view>

Page({
  data: {
    a: 1,
    b: 2,
    c: 3
  }
})

The content in view is 3 + 3 + d.

# Logical Judgments

<view wx:if="{{length > 5}}"> </view>

# String Operations

<view>{{"hello" + name}}</view>

Page({
  data:{
    name: 'MINA'
  }
})

# Data path Operations

<view>{{object.key}} {{array[0]}}</view>

Page({
  data: {
    object: {
      key: 'Hello '
    },
    array: ['MINA']
  }
})

# Combinations

You can also directly implement combinations in Mustache syntax to build new objects and arrays.

# Arrays

<view wx:for="{{[zero, 1, 2, 3, 4]}}"> {{item}} </view>

Page({
  data: {
    zero: 0
  }
})

The end result is the array [0, 1, 2, 3, 4].

# Objects

<template is="objectCombine" data="{{foo: a, bar: b}}"></template>

Page({
  data: {
    a: 1,
    b: 2
  }
})

The end result is the object {foo: 1, bar: 2}.

You can also use the extended operator ... to extend the object.

<template is="objectCombine" data="{{...obj1, ...obj2, e: 5}}"></template>

Page({
  data: {
    obj1: {
      a: 1,
      b: 2
    },
    obj2: {
      c: 3,
      d: 4
    }
  }
})

The end result is the object {a: 1, b: 2, c: 3, d: 4, e: 5}.

If the object’s key and value are identical, this can be indirectly expressed.

<template is="objectCombine" data="{{foo, bar}}"></template>

Page({
  data: {
    foo: 'my-foo',
    bar: 'my-bar'
  }
})

The end result is the object {foo: 'my-foo', bar:'my-bar'}.

Note: Any combination of the above methods is allowed, but if there are cases where identical variable names occur, the latter will overwrite the former, such as:

<template is="objectCombine" data="{{...obj1, ...obj2, a, c: 6}}"></template>

Page({
  data: {
    obj1: {
      a: 1,
      b: 2
    },
    obj2: {
      b: 3,
      c: 4
    },
    a: 5
  }
})

The end result is the object {a: 5, b: 3, c: 6}.

Note: If there are spaces between curly brackets and quotes, the content is ultimately parsed into a string

<view wx:for="{{[1,2,3]}} ">
  {{item}}
</view>

equivalent to

<view wx:for="{{[1,2,3] + ' '}}">
  {{item}}
</view>