Open up the Console in Developer Tools in any browser. For strings native methods, type
You'll get a comprehensive hierarchical listing of every kind of property.
If you want a more in-depth look at the global object, type
What this means is that when you create a string variable
var s = "string";
inferred s type is String
var s = String("string");
var s = new String("string");
String.constructor method is called to create the value "string". s prototype's is now String.prototype, and s inherits those methods, including length.