Edit in JSFiddle

// return this 가 없는 경우
function a(){
    
    this.name = 'mohwa1';
}

a.prototype.getName = function(){
    
    return this.name;
}

a.prototype.setName = function(name){
    
    this.name = name;
}

try{
    console.log(new a());
    console.log(new a().setName('mohwa1-1').getName);
}
catch(e){
    console.log(e.message);
}

        
// return this를 해주는 경우
function b(){
    
    this.name = 'mohwa2';
    
    return this;
}

b.prototype.getName = function(){
    
    return this.name;
}

b.prototype.setName = function(name){
    
    this.name = name;
    
    return this;
}		

try{
    console.log(new b());
    console.log(new b().setName('mohwa2-1').getName);
}
catch(e){
    console.log(e.message);
}