vant-weapp/packages/mixins/button.ts

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