Essentials of Javascript - Cultural View

JavaScript 3
Trademark
"JavaScript" is a trademark of Sun Microsystems. It is used under license for technology invented and implemented
by Netscape Communications and current entities such as the Mozilla Foundation. [22]
Features
The following features are common to all conforming ECMAScript implementations, unless explicitly specified
otherwise.
Imperative and structured
JavaScript supports all the structured programming syntax in C (e.g., if statements, while loops, switch statements,
etc.). One partial exception is scoping: C-style block-level scoping is not supported (instead, JavaScript has
function-level scoping). JavaScript 1.7, however, supports block-level scoping with the let keyword. Like C,
JavaScript makes a distinction between expressions and statements. One syntactic difference from C is automatic
semicolon insertion, in which the semicolons that terminate statements can be omitted. [23]
Dynamic
dynamic typing
As in most scripting languages, types are associated with values, not variables. For example, a variable x could
be bound to a number, then later rebound to a string. JavaScript supports various ways to test the type of an
object, including duck typing. [24]
object based
JavaScript is almost entirely object-based. JavaScript objects are associative arrays, augmented with
prototypes (see below). Object property names are string keys: obj.x = 10 and obj["x"] = 10 are equivalent, the
dot notation being syntactic sugar. Properties and their values can be added, changed, or deleted at run-time.
Most properties of an object (and those on its prototype inheritance chain) can be enumerated using a for...in
loop. JavaScript has a small number of built-in objects such as Function and Date.
run-time evaluation
JavaScript includes an eval function that can execute statements provided as strings at run-time.
Functional
first-class functions
Functions are first-class; they are objects themselves. As such, they have properties and can be passed around
and interacted with like any other object.
inner functions and closures
Inner functions (functions defined within other functions) are created each time the outer function is invoked,
and variables of the outer functions for that invocation continue to exist as long as the inner functions still
exist, even after that invocation is finished (e.g. if the inner function was returned, it still has access to the
outer function's variables) — this is the mechanism behind closures within JavaScript.