function-constructor

In MDN, about Functions and function scope , what does it mean by parsed every time it is evaluated ? Can this be observed by codes? Quote in the section Function constructor vs. function declaration vs. function expression : Functions defined by function expressions and function declarations are parsed only once , while those defined by the Function constructor are not . That is, the function body string passed to the Function constructor must be parsed every time it is evaluated . Although a function expression creates a closure every time, the function body is not reparsed , so function

Is there any difference in how these functions operate? The first one is more typically of what I think about when thinking of a constructor. Example 1: using this to name and set properties. Then using new to create a new Book object. function Book(name, numPages) { this.name = name; this.numPages = numPages; } var myBook = new Book('A Good Book', '500 pages'); Example 2: returning a object by using new and just calling the function itself. function Movie(name, numMinutes) { return { name:name, numMinutes:numMinutes }; } var best = new Movie('Forrest Gump', '150'); var other = Movie(