JavaScript is ...

a dynamic, weakly typed, prototype-based language with first-class functions.

JS is Dynamic

//Compilation and execution happen together.

var propMap = {
  val: "value", html: "innerHTML"
};

for(var fnName in propMap){
	
  $.prototype[fnName] = (function(prop){
  	return function(){
  	  return this[prop];
  	}
  })(propMap[fnName]);
}

JS is Weakly Typed

//Type associated with value, not variable.

var a = 1;
a = "one";
a = [1];
a = {one: 1};

JS has 1st Class Functions

//Treat like any object

var square = function(x){ return x*x },  //create

  	 mult = function(f1, f2){            // Return
    		return function(n){
      		return f1(n)*f2(n);
    		}
  	 },

  	 bigF = mult(square, square),        // ARG

value = bigF(2); // 16

JS is Prototype Based

JavaScript (JS) is a lightweight, interpreted or JIT compiled programming language with first-class functions. Most well-known as the scripting language for Web pages, many non-browser environments also use it, such as node.js and Apache CouchDB. JS is a prototype-based, multi-paradigm, dynamic scripting language, supporting object-oriented, imperative, and declarative (e.g. functional programming) styles.