how to get matching objects array of objects and json object

You can use filter method to get desired data

 var arr = {
            "oid": "1",
            "oname": "Fon",
            "bun": [{
                "bid": "1",
                "bname": "Ets",
                "dep": [{
                    "did": "1",
                    "dname": "Dptment",
                    "pids": [{
                        "pid": "1",
                        "st": "active"
                    }, {
                        "pid": "2",
                        "st": "active"
                    }]
                }]
            }, {
                "bid": "2",
                "bname": "US",
                "description": "unit2",
                "dep": []
            }]
        }

var oname = arr.oname;
var data = arr.bun.filter(function (a) { return a.bid == "1" });

You can use filter to get a subset of only the data you want:

data.bun.filter(function(d){ if( d.bid == 1 ) return true; } );

Create a new object with the data you wish to have

var newObj = {
   "oname": data.oname, 
   "bun": data.bun.filter(function(d){ if( d.bid == 1 ) return true; } ) 
};

You can use bracket notation in javascript for this like

var key = "oname";
var value = json[key];