var w = 'a||a1||a2,b||b1,c||c1||c2,a';function start(str) {    var strArr = str.split(',');    var selectedArr = [];    var selectedMap = {};    strArr.map(function (v) {        return v.split('||');    }).forEach(function (v) {        var parent;        var parentCode;        var child;        var childCode;        var childrenArr;        var len = v.length;        if (len === 1) {            parentCode = v[0];            parent = selectedMap[parentCode];            if (!parent) {                genObj(selectedMap, selectedArr, parentCode);            }        } else {            for (var i = 1; i < len; i++) {                parentCode = v[i - 1];                parent = selectedMap[parentCode];                if (!parent) {                    childrenArr = selectedArr;                    genObj(selectedMap, childrenArr, parentCode);                    parent = selectedMap[parentCode];                }                childCode = v[i];                childrenArr = parent.children;                genObj(selectedMap, childrenArr, childCode);            }        }    })        return selectedArr;}console.log(JSON.stringify(start(w)));