Wait... What are you trying to achieve here?
I think you're after something like this?
var json = {9: "1", 2: "4", 6: "5", 7: "3", undefined: ""};
var questionId = 9;
var answer = 2;
var comparison = '<';
var result = null;
if (json.hasOwnProperty(questionId)) {
if (comparison === '<') {
result = json[questionId] < answer;
}
if (comparison === '>') {
result = json[questionId] > answer;
}
if (comparison === '=') {
result = json[questionId] == answer;
}
}
console.log(result);