Will Klein

JS looks like C

C has block-level scoping

JS has function-level scoping

JS is not C

var f = function() {    var a = 1;    if (true) {        var a = 2;    }    return a; // 2};

a is scoped to its parent scope, function f

if, for, while, etc. blocks don't get their own scope

var g = function() {
    b = 1;
    var b = b + 2;
    return b; // 3
};

b is scoped to its parent function g

The above is equivalent to:

var g1 = 'g1 is a global';g2 = 'g2 is a global';
(function() {    var l = 'This is local';    g3 = 'g3 is also a global';})();

Missing a var creates a global!

Don't mind the IIFE:

var a = 1; // a: 1
(function() {
    var a = 2 // a: 2
    (function() {
        var a = 3; // a: 3
    })();        (function(a) {        // a: 4    })(4);
})();
// a: 1

a exists uniquely in each scope

(function() {
    var a = 1;

    (function() {
        a++;
    })();
    // a: 2
})();

This is a basic closure

var count = (function() {
    var count = 0;

    return function() {
        count = count + 1;
        return count;
    };
})();
count(); // 1
count(); // 2

A more useful closure

@willslab

http://willkle.in

github.com/willklein