ES5 Object.assign equivalent

In underscore.js you can use like,

_.extend(firstObj, secondObj);

In jQuery, you can use,

$.extend({},firstObj,secondObj);

In pure javascipt, you can merge n number of objects by using this function:

function mergeObjects() {
    var resObj = {};
    for(var i=0; i < arguments.length; i += 1) {
         var obj = arguments[i],
             keys = Object.keys(obj);
         for(var j=0; j < keys.length; j += 1) {
             resObj[keys[j]] = obj[keys[j]];
         }
    }
    return resObj;
}