Question

How to detect if a function is called as constructor in Javascript?

Answer 1

You can use new.target pseudo-property to detect whether a function was called as a constructor(using the new operator) or as a regular function call.

1. If a constructor or function invoked using the new operator, new.target returns a reference to the constructor or function.
2. For function calls, new.target is undefined.

function Myfunc() {
  if (new.target) {
    console.log("called with new");
  } else {
    console.log("not called with new");
  }
}

new Myfunc(); // called with new
Myfunc(); // not called with new
Myfunc.call({}); // not called with new