What five JavaScript concepts do I need to understand to be a good AngularJS developer?

1. the type system: there are two fundamentally different kinds of values: primitives and objects. Number, string, boolean, null, undefined are all primitives.
   Array ( [1,2,3] ), object ( { prop1: value1, prop2: value2 } ), and function are all objects.
2. prototypal inheritance – this is especially important when you attempt to databind in AngularJS to a primitive
3. array['syntax'] === array.syntax; array['$id'] === array.$id; array[someExpression] has no eqivalent "." notation
4. variable scope and assignment
   • a variable defined anywhere inside a function is visible everywhere inside that function
   • when a variable is assigned an object, it is assigned a reference (not a copy). This becomes important in AngularJS when, e.g., you fetch JSON data from a server and you assign the results to a variable. This resets the reference. Other variables (say in your controller) that point to the old reference continue to point to the old reference. (example)
5. closures – these are very useful when defining AngularJS services (example) and when defining methods on a controller using this (example)

Also note that JavaScript is single-threaded!