Efficient data storage on Ruuvitag

Hey, I'm not sure if this is the right place to ask but I'm having a problem combining two Espruino/JavaScript concepts on my RuuviTag sensor beacon and I was wondering if anyone here had any insight into the matter.
Basically, I'm trying to use a variation of the program on this web page: [https://lab.ruuvi.com/temp-logger/]

But I'm trying to modify it so that I can store a lot more values by lowering the precision and storing values that take up less space in the RuuviTag memory.
For that purpose I found this Espruino method which supposedly lets you store sensor reading as 8 bit integers instead of 32 or 64 bit floats: [https://www.espruino.com/Data+Collection]
Here is what I have right now:

const period = 1000; // milliseconds (every 30 minutes)
const length = 10; // number of records (for 100 hours / 4 days)

var ruuvi = require("Ruuvitag");
var records = new Int8Array(length);

function log() {
  ruuvi.setEnvOn(true);
  if (records.unshift({time:getTime(),temp:ruuvi.getEnvData().temp}) > length){
    records.pop();
  }
  ruuvi.setEnvOn(false);
}

function getData() {
  records.forEach( function(d,i) {
    console.log(i+"\t"+ d.temp +"\t"+ (getTime()-d.time));
  });
}

ruuvi.setAccelOn(true);
setInterval(log, period);

When I upload and run this code it says this over and over:

in function called from system
Uncaught Error: Function "unshift" not found!
 at line 2 col 15
  if (records.unshift({time:getTime(),temp:ruuvi.getEnvData(...
              ^

And when I type the getData() command into the left side while the program is running I get this:

in function called from system
>getData()
0	undefined	NaN
1	undefined	NaN
2	undefined	NaN
3	undefined	NaN
4	undefined	NaN
5	undefined	NaN
6	undefined	NaN
7	undefined	NaN
8	undefined	NaN
9	undefined	NaN
=undefined

Am I missing something about the code? Or is it harder than I think it is to log values that take up less space in the memory? I don't see any reason why the unshift function would not be found. If unshift won't work for this type of operation, is there something else that will?