Things to clear up before jumping into the world of React

new-keyword.md

2. How "new" keyword works in JS

  function Dog(name) {
    if (name) { this.name = name; }
    this.speak = function() {
        return this.name + " says woof";
    }
  }

  var v = new Dog("Vincent");

When we call the Dog function with the new keyword we are asking JavaScript to do three things:

1. Create an empty object;
2. Set the new object's prototype to point to the Dog.prototype;
3. And call the constructor method on the new object.

  var v = Object.create(Dog.prototype);
  v.constructor("Vincent");

  v.speak();  // "Vincent says woof"

The first line above creates an empty object and sets its prototype to equal the first argument, in this case Dog.prototype. The second line simply executes the constructor method on the object, which now points to the Dog function.

If you want to go more in depth, please refer to this!