vant-weapp/dist/mixins/button.js

export var button = Behavior({
  properties: {
    id: String,
    sessionFrom: String,
    appParameter: String,
    sendMessageImg: String,
    sendMessagePath: String,
    showMessageCard: String,
    sendMessageTitle: String,
    lang: {
      type: String,
      value: 'en'
    }
  }
});