Full JavaScript Object Model and Lexical Closures Overview
Explore the JavaScript Object Model with examples on mapping strings to values, functions as first-class objects, and method properties. Delve into full lexical closures with a factorial function implementation. Understand JavaScript's permissiveness and object property manipulation.
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Presentation Transcript
Universit di Pisa JavaScript Object Model Giuseppe Attardi
JavaScript in two slides Objects map strings to values (properties): var obj = new Object; obj["prop"] = 42; obj["0"] = hello ; Functions are first-class objects: function fact(n) { return (n == 0) ? 1 : n * fact(n-1); } fact.desc = "Factorial function"; => obj.prop => obj[0]
JS in two slides (2) So methods are function-valued properties: obj.frob = function (n) { this.prop += n; }; obj.frob(6); Permissiveness throughout. Oops. grob = obj.frob; grob(6); prop = hello ; grob(6); => obj.prop == 48 => var not necessary => undefined + 6 == NaN => reset global prop => prop == hello6
Full Lexical Closures Y = f. ( x. xx) ( x. f( v. (xx) v) Yfv = f(Yf) v function Y(f) { return function (x) { return x(x); }( function (x) {return f(function (v) { return x(x)(v); }); }); } var fact = Y(function (fact) { return function (n) { return (n == 0) ? 1 : n * fact(n-1); } }); fact(5); => 120
