Simple ready checker (simple deferred) + Dom ready Checker

ready-checker.js

var ReadyChecker = (function () {
    /**
     * Simple Deferred
     * @param {Function} readyCheckerResolver
     * @param {Function} [callback]
     * @constructor
     */
    function ReadyChecker (readyCheckerResolver, callback) {
        this.onReady(callback)

        var _this = this

        if (typeof readyCheckerResolver === 'function') {
            readyCheckerResolver(function() {
                _this.resolve.apply(_this, arguments)
            })
        }

        return this
    }

    ReadyChecker.prototype.onReady = function (callback) {
        if (this.isReady) {
            runCallback(callback, this._resolvedContext)

            return this
        }

        this.onReadyCallbacks = this.onReadyCallbacks || []

        if (typeof callback == 'function') {
            this.onReadyCallbacks.push(callback)
        }

        return this
    }

    /**
     * @param [context]
     * @returns {ReadyChecker}
     */
    ReadyChecker.prototype.resolve = function (context) {
        if (this.isReady) {
            return this
        }

        this.isReady = true
        this._resolvedContext = context

        runCallback.call(this, this.onReadyCallbacks, this._resolvedContext)

        return this
    }

    var runCallback = function (callbacks, context) {
        if (typeof callbacks === 'function') {
            callbacks = [callbacks]
        }

        if (!(callbacks instanceof Array)) {
            return
        }

        if (callbacks.length) {
            var i

            for (i in callbacks) {
                if (!callbacks.hasOwnProperty(i)) {
                    continue
                }

                var readyCallback = callbacks[i]

                if (typeof readyCallback === 'function') {
                    readyCallback.call(context || window)
                }

                callbacks.splice(i)
            }
        }
    }

    return ReadyChecker
})();

// Usage:

/**
 * Simple DOM Ready checker
 * @param callback
 */

var domReadyChecker

function domReady (callback) {
    // Any DOM_Ready checker
    domReadyChecker = domReadyChecker || new ReadyChecker(function (ready) {
        if (document.readyState === 'complete') {
            ready()

            return
        }

        if (document.addEventListener) {
            var pageReadyEvent = function () {
                document.removeEventListener('DOMContentLoaded', pageReadyEvent, false)
                window.removeEventListener('load', pageReadyEvent, false)

                ready()
            }

            document.addEventListener('DOMContentLoaded', pageReadyEvent, false)
            window.addEventListener('load', pageReadyEvent, false)
        }
    })

    domReadyChecker.onReady(callback)
}