sample code

    var NUMBER = 0;

    function chromeExpansionFn(str){
        return JSON.stringify(JSON.stringify(str));
    }

    function syncStore(key, objectToStore, callback) {
        function afterStorageClear(){
            storage.set(storageObj, function(){
                var lE = chrome.runtime.lastError;
                if(lE){
                    console.log("error " + lE.message + " received at " + NUMBER);
                    console.log("retrying with NUMBER = " + (NUMBER+=1));
                    syncStore(key, objectToStore, callback);
                }
                else {
                    console.log("didn't get any error at NUMBER = " + NUMBER);
                    if(callback) callback();
                }
            });
        }

        var jsonstr = JSON.stringify(objectToStore), i = 0, storageObj = {},
            // (note: QUOTA_BYTES_PER_ITEM only on sync storage)
            // subtract two for the quotes added by stringification
            maxBytesPerItem = storage.QUOTA_BYTES_PER_ITEM - NUMBER,
            // since the key uses up some per-item quota, use
            // "maxValueBytes" to see how much is left for the value
            maxValueBytes, index, segment, counter;

        console.log("jsonstr length: " + lengthInUtf8Bytes(jsonstr));
        console.log("after stringification: " + lengthInUtf8Bytes(chromeExpansionFn(jsonstr)));

        // split jsonstr into chunks and store them in an object indexed by `key_i`
        while(jsonstr.length > 0) {
            index = key + "_" + i++;
            maxValueBytes = maxBytesPerItem - lengthInUtf8Bytes(index);

            counter = maxValueBytes;
            segment = jsonstr.substr(0, counter);

            console.log("SEGEMENT BEFORE CHOPPING:");
            //console.log(segment);
            console.log(segment.length);
            console.log(lengthInUtf8Bytes(chromeExpansionFn(segment)), maxValueBytes);

            while(lengthInUtf8Bytes(chromeExpansionFn(segment)) > maxValueBytes)
                segment = jsonstr.substr(0, --counter);

            console.log("SEGEMENT AFTER CHOPPING:");
            console.log(segment.length);
            console.log(lengthInUtf8Bytes(chromeExpansionFn(segment)), maxValueBytes);

            storageObj[index] = segment;
            jsonstr = jsonstr.substr(counter);
        }
        // later used by retriever function
        storageObj[key] = i;
        console.log((i + 1) + " keys used (= key + key_i)");
        // say user saves till chunk 20 in case I
        // in case II, user deletes several snippets and brings down
        // total no. of "required" chunks to 15; however, the previous chunks
        // (16-20) remain in memory unless they are "clear"ed.
        storage.clear(afterStorageClear);
    }