<textarea class="textarea-box" value="{{plan}}" placeholder="" maxlength="500" disable-default-padding="{{isIos}}" bindinput="monitorPlanInput"></textarea>

    let phone = wx.getSystemInfoSync();  //调用方法获取机型
    let isIos = null
    if (phone.platform == 'ios') {
        isIos = true
    } else if (phone.platform == 'android') {
        isIos = false
    }
    this.setData({
      isIos
    })

disable-default-padding="true"的时候去掉微信小程序的textarea在ios默认的padding值