Uncaught TypeError: Assignment to constant variable.

[Blatman]

I get this error when trying to use setBrightnessLevel and setCustomGammaCurve

Uncaught TypeError: Assignment to constant variable .... (@ dcraw.js:4)

Just seems to me that only the boolean options work with this code unless I am missing a trick with the syntax.
All the examples are with booleans as well

Tried -

var result = dcraw(buf, { setBrightnessLevel: 1.0 });  - fails and this is default
var result = dcraw(buf, { setBrightnessLevel: '1.0' });  - fails


var result = dcraw(buf, { setCustomGammaCurve: 2.4 12.92 }}); - fails
var result = dcraw(buf, { setCustomGammaCurve: 2.4, 12.92 }}); - fails
var result = dcraw(buf, { setCustomGammaCurve: '2.4', '12.92' }}); - fails
var result = dcraw(buf, { setCustomGammaCurve: { p: 2.4, ts: 12.92 }}); - fails


var result = dcraw(buf, { exportAsTiff: true }); - works OK 
var result = dcraw(buf, { extractThumbnail: true }); - works OK
var result = dcraw(buf, { });  // PPM - works OK
var result = dcraw(buf, { useRawMode: true });  - works OK

Cheers,

Blane