Check if a property exist for an object

If you use the Object Spy tool, it will list all the exposed properties of the UI Object.

Or do you mean verifying a property, if so, see aqObject.CompareProperty Method

See aqObject.CheckProperty Method 

Hopefully, I understand what you mean now. Try this,

function CheckProperty()
 {
     const Name = {
         Firstname: "SmartBear"
     }
     
     Log.Message(Name.Firstname);
     Log.Message(Name.hasOwnProperty("Firstname")); // true
     Log.Message(Name.hasOwnProperty("Surname"));   // false
 }

Use "hasOwnProperty()"

Hi,

> if an HTML object has a specific property

I believe that you are looking for how to check if HTML object (actually - html markup for the given element) has not a specific property, but some specific attribute, aren't you?

In this case use the .hasProperty() html built-in method accessible from within TestComplete.

https://developer.mozilla.org/en-US/docs/Web/API/Element/hasAttribute

https://www.w3schools.com/jsref/met_element_hasattribute.asp

Use this method : 

//javascript

var hasProperty = aqObject.IsSupported(obj, "property_name");

if "hasProperty" is true, then the property is available on your object and you can interact with. If false, then the property does not exist in your object.