global-local-capture.js

'use strict';

var globalFoo;

function Foo(name) {
    this.name = name;
}

function captureGlobalFoo(name) {
    globalFoo = new Foo(name);

    return function () {
        return globalFoo;
    }
}

function captureLocalFoo(name) {
    var localFoo = new Foo(name);

    return function () {
        return localFoo;
    }
}

var alpha = captureGlobalFoo('alpha');
var  beta = captureGlobalFoo('beta');

var gamma = captureLocalFoo('gamma');
var delta = captureLocalFoo('delta');

console.log('alpha', alpha());
console.log(' beta', beta());
console.log('gamma', gamma());
console.log('delta', delta());

// Outputs:
//
// alpha { name: 'beta' } <-- we've lost Foo('alpha').
//  beta { name: 'beta' }
// gamma { name: 'gamma' }
// delta { name: 'delta' }
//
// The closure created by captureGlobalFoo(...) captured the mutable globalFoo
// and not its particular value at the time the closure was created.