[{ GroupMark: "", GroupName: "hao", SendTime: '123', SendContent: "1ha" },

{ GroupMark: "1", GroupName: "hao", SendTime: '123', SendContent: "2ha" },

{ GroupMark: "1", GroupName: "hao", SendTime: '123', SendContent: "3ha" },

{ GroupMark: "22", GroupName: "hao", SendTime: '123', SendContent: "4ha" },

{ GroupMark: "3", GroupName: "hao", SendTime: '123', SendContent: "6ha" },

{ GroupMark: "22", GroupName: "hao", SendTime: '123', SendContent: "5ha" }]

[{"GroupMark":"","GroupName":"hao","SendTime":"123","SendContent":["1ha"]},
{"GroupMark":"1","GroupName":"hao","SendTime":"123","SendContent":["2ha","3ha"]},
{"GroupMark":"22","GroupName":"hao","SendTime":"123","SendContent":["4ha","5ha"]},
{"GroupMark":"3","GroupName":"hao","SendTime":"123","SendContent":["6ha"]}]

//参照数组去重的
var arr =[{ GroupMark: "", GroupName: "hao", SendTime: '123', SendContent: "1ha" },

{ GroupMark: "1", GroupName: "hao", SendTime: '123', SendContent: "2ha" },

{ GroupMark: "1", GroupName: "hao", SendTime: '123', SendContent: "3ha" },

{ GroupMark: "22", GroupName: "hao", SendTime: '123', SendContent: "4ha" },

{ GroupMark: "3", GroupName: "hao", SendTime: '123', SendContent: "6ha" },

{ GroupMark: "22", GroupName: "hao", SendTime: '123', SendContent: "5ha" }]

var tempObj ={}

var resArr = []

for(let [index,item] of arr.entries() ){

    let {GroupMark,GroupName,SendContent} = item

    let keyStr = GroupMark+'&'+GroupName

    if(tempObj[keyStr]){

        let tempSendContent= tempObj[keyStr].SendContent

        tempObj[keyStr].SendContent=[...tempSendContent,SendContent]

    }else{

        tempObj[keyStr]={

            ...item,

            SendContent:[SendContent]

        }

    }

}

for (let item in tempObj) {

    resArr.push(tempObj[item])

}

console.log(resArr)