memoization.js

ko.memoization = (function () {
    var memos = {};

    function randomMax8HexChars() {
        return (((1 + Math.random()) * 0x100000000) | 0).toString(16).substring(1);
    }
    function generateRandomId() {
        return randomMax8HexChars() + randomMax8HexChars();
    }
    function findMemoNodes(rootNode, appendToArray) {
        if (!rootNode)
            return;
        if (rootNode.nodeType == 8) {
            var memoId = ko.memoization.parseMemoText(rootNode.nodeValue);
            if (memoId != null)
                appendToArray.push({ domNode: rootNode, memoId: memoId });
        } else if (rootNode.nodeType == 1) {
            for (var i = 0, childNodes = rootNode.childNodes, j = childNodes.length; i < j; i++)
                findMemoNodes(childNodes[i], appendToArray);
        }
    }

    return {
        memoize: function (callback) {
            if (typeof callback != "function")
                throw new Error("You can only pass a function to ko.memoization.memoize()");
            var memoId = generateRandomId();
            memos[memoId] = callback;
            return "<!--[ko_memo:" + memoId + "]-->";
        },

        unmemoize: function (memoId, callbackParams) {
            var callback = memos[memoId];
            if (callback === undefined)
                throw new Error("Couldn't find any memo with ID " + memoId + ". Perhaps it's already been unmemoized.");
            try {
                callback.apply(null, callbackParams || []);
                return true;
            }
            finally { delete memos[memoId]; }
        },

        unmemoizeDomNodeAndDescendants: function (domNode, extraCallbackParamsArray) {
            var memos = [];
            findMemoNodes(domNode, memos);
            for (var i = 0, j = memos.length; i < j; i++) {
                var node = memos[i].domNode;
                var combinedParams = [node];
                if (extraCallbackParamsArray)
                    ko.utils.arrayPushAll(combinedParams, extraCallbackParamsArray);
                ko.memoization.unmemoize(memos[i].memoId, combinedParams);
                node.nodeValue = ""; // Neuter this node so we don't try to unmemoize it again
                if (node.parentNode)
                    node.parentNode.removeChild(node); // If possible, erase it totally (not always possible - someone else might just hold a reference to it then call unmemoizeDomNodeAndDescendants again)
            }
        },

        parseMemoText: function (memoText) {
            var match = memoText.match(/^\[ko_memo\:(.*?)\]$/);
            return match ? match[1] : null;
        }
    };
})();

ko.exportSymbol('memoization', ko.memoization);
ko.exportSymbol('memoization.memoize', ko.memoization.memoize);
ko.exportSymbol('memoization.unmemoize', ko.memoization.unmemoize);
ko.exportSymbol('memoization.parseMemoText', ko.memoization.parseMemoText);
ko.exportSymbol('memoization.unmemoizeDomNodeAndDescendants', ko.memoization.unmemoizeDomNodeAndDescendants);