function installPostMessageImplementation()

in www/benchmarks/setImmediate.js [145:180]

• 5 lines of code
• 1 McCabe index (conditional complexity)

    function installPostMessageImplementation(attachTo) {
        // Installs an event handler on `global` for the `message` event: see
        // * https://developer.mozilla.org/en/DOM/window.postMessage
        // * http://www.whatwg.org/specs/web-apps/current-work/multipage/comms.html#crossDocumentMessages

        var MESSAGE_PREFIX = "com.bn.NobleJS.setImmediate" + Math.random();

        function isStringAndStartsWith(string, putativeStart) {
            return typeof string === "string" && string.substring(0, putativeStart.length) === putativeStart;
        }

        function onGlobalMessage(event) {
            // This will catch all incoming messages (even from other windows!), so we need to try reasonably hard to
            // avoid letting anyone else trick us into firing off. We test the origin is still this window, and that a
            // (randomly generated) unpredictable identifying prefix is present.
            if (event.source === global && isStringAndStartsWith(event.data, MESSAGE_PREFIX)) {
                var handle = event.data.substring(MESSAGE_PREFIX.length);
                tasks.runIfPresent(handle);
            }
        }
        if (global.addEventListener) {
            global.addEventListener("message", onGlobalMessage, false);
        } else {
            global.attachEvent("onmessage", onGlobalMessage);
        }

        attachTo.setImmediate = function () {
            var handle = tasks.addFromSetImmediateArguments(arguments);

            // Make `global` post a message to itself with the handle and identifying prefix, thus asynchronously
            // invoking our onGlobalMessage listener above.
            global.postMessage(MESSAGE_PREFIX + handle, "*");

            return handle;
        };
    }