Question

my problem here that i don’t understand how does the method called “objectchanger” works
here is the source

function test()
{
  this.value=5;
}

test.prototype.Add=function()
{
  this.value++;
};

var obj = new test();

obj.Add();

alert(obj.value);


function objectchanger(fnc, obj)
{
  fnc.call(obj); 
  //obj.fnc(); >> without this line of code it works fine but why?????
  //why i don't need to write this code --
}

objectchanger(obj.Add, obj);
alert(obj.value); // the value is now 7 

Answer 1

call is a method on the Function object. It calls a function with the passed-in object as the this value in the function. See the MDN docs on call.

So when objectchanger calls fnc.call(obj), it is calling test.prototype.Add.call(obj), which is the same as calling obj.Add().