20x4 display and big_number not working ?

Display works fine on I2C. Trying this code

I2C1.setup({scl:B6, sda:B7});
var lcd = require("HD44780").connectI2C(I2C1);

// var lcd = ... from simple example above ...
var disp = require("big_number").use(lcd);
// fill the screen with '12345'
disp.showNumber(12345);
// or draw just the digits you want, where you want

but get this ..

 _____                 _ 
|   __|___ ___ ___ _ _|_|___ ___ 
|   __|_ -| . |  _| | | |   | . |
|_____|___|  _|_| |___|_|_|_|___|
          |_| http://espruino.com
 1v60 Copyright 2014 G.Williams
>echo(0);
ERROR: Function not found! Skipping. at line 2 col 1
showDigit(17,a%10);9<a&&showDigit(14,a/10%10);99<a&&showDigit(11,a/100%10);999<a&&showDigit(8,a/1E3%10);9999<a&&showDigit(5,a/1E4%10)}
 ^
at line 2 col 10
showDigit(17,a%10);9<a&&showDigit(14,a/10%10);99<a&&showDigit(11,a/100%10);999<a&&showDigit(8,a/1E3%10);9999<a&&showDigit(5,a/1E4%10)}
          ^
in function "showNumber" called from line 1 col 22
=undefined
> 

Any ideas ?