cell render value is undefined

[BDavis]

I am using a cell renderer, and when assigning the cell value to a var used by my script, the var shows as undefined, even though the celldata.value shows a valid string.  The basics of the js code are:

canRender: function (cellData) {
console.log("cellData.field ", cellData.field);
if (cellData.field === 'audiofiles') {
return true;
}
else {
return false;
}

render: function ($td, cellData) {
console.log("cellData.value ", cellData.value);
var mysoundfiles = cellData.value.tostring;
console.log("mysoundfiles ", mysoundfiles);

and the results from the console log are:

cellData.field last_audio       

cellData.field audiofiles
cellData.value (3) ['LOWRATES.wav RES1.wav', 'RES1.WAV CATSTROP.WAV', 'TLPRESNAP.wav']
mysoundfiles undefined

when trying to use the cellData.value,  it always returns 'undefined'

Oddly, this code was working at one time, then just stopped working for some reason. 

Any help is greatly appreciated! ..