Fundamental Difference between fn() and new fn() in javascript

Question

In what all aspects, calling a function with and without new keyword differ in javascript? I mean what all things are differing between?

testFn() vs new testFn()

Answer 1

new creates a new (empty) object and sets this to it, then calls the function, which acts as the constructor for the object (by manipulating this.something). Calling the same function without the new keyword would let it act on whatever this currently means.

Answer 2

These variants are syntactically different: with "new" variant supposes that the function is a constructor. The variant without "new" supposes, that it is not a constructor.