Merging two js objects without jquery

mergeObjects.es6.js

Object.prototype.assign = Object.assign || function(obj1, obj2) {
    var obj3 = obj1;

    for (var attrname in obj2) {
        if (typeof(obj2[attrname]) !== 'function') {
            obj3[attrname] = obj2[attrname];
        }
    }

    return obj3;
};