Private state with prototypes, using weakMap

by ScottRippey

JavaScript

var Person = (function() {
    var _ = weakMap();
    var Person = function(first, last) {
        _(this).firstName = first;
        _(this).lastName = last;
    }
    Person.prototype = {
        fullName: function() {
            return _(this).firstName + _(this).lastName;
        },
        firstName: function() {
            return _(this).firstName;
        }
    };
    return Person;
})();

function weakMap() {
    var instances=[], values=[];
    return function(instance, destroy) {
        var index = instances.indexOf(instance);
        if (destroy) {
            // Delete the private state:
            instances.splice(index, 1);
            return values.splice(index, 1)[0];
        } else if (index === -1) {
            // Create the private state:
            instances.push(instance);
            values.push({});
            return values[values.length - 1];
        } else {
            // Return the private state:
            return values[index];
        }
    };
}