I think the following solution should be added: 1. It is shorter 2. use of prototype is not something necessary for that specific question spirit, maybe question should be improved var key, obj = { name: 'john', surname: 'doe' }; for (key in obj) { if (obj.hasOwnProperty(key)) { if (key != "name") { console.log(key + ' exists in obj'); console.log(key + ': ' + obj[key]); continue; } else console.log(key + " doesn't exist in obj"); } }