I took the example from this question modified a bit:
What is the point of the prototype method?
function employee(name,jobtitle,born)
{
this.name=name;
this.jobtitle=jobtitle;
this.born=born;
this.status="single"
}
employee.prototype.salary=10000000;
var fred=new employee("Fred Flintstone","Caveman",1970);
console.log(fred.salary);
fred.salary=20000;
console.log(fred.salary)
And the output in console is this:
What is the difference salary is in constructor but I still can access it with fred.salary, how can I see if is in constructor from code, status is still employee property how can I tell for example if name is the one of employee or has been touch by initialization?
Why is salary in constructor, when name,jobtitle,born where “touched” by employee("Fred Flintstone","Caveman",1970); «constructor»?
By setting the prototype, you are just making an object to be shared with other instances of the same type. ie,
var liz = new employee('Elizabeth','Teacher',1980);
var jane = new employee('Jane','unknown',1981);
liz.salary is same as jane.salary, even the underlying memory will be the same.
but when you set the salary of an instance, you are not changing the salary variable in the prototype, but you are defining a new property unique for that instance. so, fred.salary = 20000 will just hide the salary attribute of the prototype.
so fred.salary will make javascript engine to look for salary in the fred instance tree, upon which it will take the direct property of that instance.
while liz.salary will resolve to the property in the prototype.
I hope now the console output make some sense.
1