How to bind json stringify data in golang custom struct type?

js ajax

$.ajax({
    type: "POST"
    , url : url
    , data : JSON.stringify('{"nowBlockPositionX":3,"nowBlockPositionY":0,"nowBlock":{"O":0}}')
})

go custom struct

type demo struct {
    nowBlockPositionX  int                `form:"nowBlockPositionX" json:"nowBlockPositionX"`
    NowBlockPositionY  int                `form:"nowBlockPositionY" json:"nowBlockPositionY"`
    NowBlock           map[string]int     `form:"nowBlock" json:"nowBlock" query:"nowBlock"`
}


don't binding this

demo := new(demo)
if err := c.Bind(demo); err != nil {
    c.Logger().Error(err)
}