Running code off of an EEPROM

... string data store ... went over my head on the first read

No wonder, you were at that time deep down in the details of the HW of EEPROMS. Coming back up into application (close) layers, it will be a breeze for you (and you may tell me where my doc needs to be fixed/enhanced, since I'm not of English mother tongue nor eloquent writer... JS is closer to me than English).

over my head

I'm fairing about the same way when looking on things coming out of your fine 'micro brewery' - on first reads. After taking the time diving into it, I get the exquisite taste. Thanks for your contributions!

the writes will of course be slow

Speed in accessing FRAM/MRAM depends on the needs of the application. To get/set config data and user data, the current speed is good enough, because the amount of data is not that critical - and there is most of the time little visibility to the user - if there is even one - to notice and complain about sluggishness. Speed is required only in graphics because of the amount of data and because visibility. My code to communicate with the FRAM was quite similar to your EEPROM code, even with the size limit because of (simplified) 2 bytes addressing with (singed) int. I can easily see speeding up the memory read/write process by using "compiled"; option, or moving the critical code into assembler all together... especially the part that shows patterns for what DMA was implemented: get a particular amount data at a particular address from one SPI (or other wise connected) device to another one (and back), like in my graphical app where screen buffer has to be saved for an overlay/pop-up - and then restored. For fast handling of those transfers, some chips have the hold pin, which keeps state, while the partial data just read is written to the other device... I was thinking along these lines to have some software DMA module implemented:

// devA & devB setup & connected, such as LCD display, (serial) RAM/EEPROM, etc.
// both implementing same kind of read/write interface
var dmaAB = require("DMA").connect(devA,devB,memBufSize); // w/ req/conn pattern
var DMA = require("DMA"); var dmaAB = new DMA(....); // w/ oo/class req/conn 
dmaAB.xfer(0,addr1,bytes,addr2); // xfers bytes in memBufSize chunks from A to B
dmaAB.xfer(1,addr2,bytes,addr1); // xfers bytes in memBufSize chunks from B to A

I can picture to use DMA on an intermediating Espruino in the data line between just any 'devices': sensors and internet... etc. I can also picture an option where the dma is setup to be trigger by a sourcing device to transfer the data to the sinking one... (...with the classical 'null' device...

Piggy-backing existing (module) code with extending or overwriting is always an option, and if this is not good enough or too cumbersome, I could see different implementations for a particular layer in the existing software stack... assuming it is layered/a stack and not a monolith... ;-). On a micro - on the other hand - a few terse, dedicated modules go further than larger, elaborate multi-purpose components. Therefore, a good and easy way to compose all kinds of needed specific functions and just those form very smaller ones is key, and require("module") is the key enabler for that.

Try using my AT25 module to interface with your FRAM

My FRAM is soldered onto my Espruino board. Will re-jumper-cable it and and do some testing, and also look at my x-code for the string memory. The string memory x-code needs transformation towards the available memory read/write interface with its data converters before I go and move it onto Espruino. I'd like to have also a test-bed/test for the sting memory store. And last but not least, implement an optional key function: store and read back by key rather than physical address (related object id)... even if it is just to get those physical addresses of the objects on init after a (re)boot.