var students=[
{name: "vehicleTravelLicenseCopyBack", id: "a1"},
{name: "vehicleTravelLicenseCopyFront", id: "a2"},
{name: "idCardBack", id: "a3"},
{name: "idCardFront", id: "a4"}
]
var arr=[];
for(var i=0;i<students.length;i++){
arr.push(students[i]['id']);
}
console.log(arr,'4555');