javascript object properties is not displaying -

i have below javascript function-

function responseval() {     this.value1;     this.value2; }    var response = new responseval(); 

i tried , execute above code in chrome consolebar.i not understand why newly created object "response" not show property value1 , value2. can me understand happening , why properties not displaying.

declaring property without setting nothing. while won't result in error, interpreters throw warning—as strict mode, believe.

javascript doesn't make obvious. example, if this:

function hello() {      this.value1; }  var h = new hello; alert(h.value1); 

the alert read undefined. however, property value1 never accessed—it doesn't exist @ because did not provide value it.

rather throwing error, javascript returns undefined time try access property doesn't exist. same result if write, say:

alert(h.property_that_doesnt_exist);   //alerts 'undefined' 

iterating through properties of h shows property value1 not exist:

for (var key in h) {     alert(key + ' = ' + h[key]); } 

this alerts nothing, because no properties found. however, if set property js primitive undefined, property exist:

function hello() {      this.value1 = undefined; }  var h = new hello;  (var key in h) {     alert(key + ' = ' + h[key]);  //alerts 'undefined' } 

you can run above code here: http://jsfiddle.net/acdmn/

---

but there's no reason set property/variable undefined. create property "empty" value, javascript programmers typically use null:

function hello() {      this.value1 = null; } 

this makes clear property created intentionally, you're not ready give meaningful value yet.

---

lastly, note property definitions work differently "normal" (private) variables explicitly set var (even though these properties, in case of window object). if write:

var foo; alert(foo); alert(some_undefined_variable_name); 

the first alert undefined. variable foo was created, exist, , contains primitive value undefined (even though didn't set explicitly). second alert, however, throw reference error:

referenceerror: some_undefined_variable_name not defined 

so javascript unforgiving using undefined variables, doesn't care if try use undefined property.