wxml:<picker mode=“date” value="{{nowDateString}}" start=“1970-01-01” end=“2020-01-01”></picker>

js:

onLoad: function () {

        var nowDate = new Date();

        var year = nowDate.getFullYear(), month = nowDate.getMonth() + 1, day = nowDate.getDate()

        this.setData({

            “nowDateString”: `${year}-${month}-${day}`

        })

    }