without Map

HTML

<script>
    
    var _consoleLog = console.log;
    
    console.log = function(){
        var name = _consoleLog.apply(console,arguments);
        var str = "";
        for(var index in arguments){
            if(Array.isArray(arguments[index])){
               arguments[index] = arguments[index].map(function(item){
                    if(typeof item == "object"){
    item = JSON.stringify(item,null,4)+"<br>";
                    }
    
                    return item;
               });
               str += arguments[index]+" ";
                
            } else if(typeof arguments[index] == "object"){
                str = JSON.stringify(arguments[index],null,4);
            } else {
                str += arguments[index]+" ";
            }
        }
    $('body').append("<div>"+str+"</div>");
    }
   
</script>

JavaScript

var oldArr = [{first_name:"Colin",last_name:"Toh"},{first_name:"Addy",last_name:"Osmani"},{first_name:"Yehuda",last_name:"Katz"}];

function getNewArr(){
        
    return oldArr.map(function(item,index){
        item.full_name = item.first_name;
        console.log(item.full_name);
        return item.full_name;
    });
    
}

console.log(getNewArr());