Script running in toolkit but fails in Illustartor

I have a script that loops through items on the page, then depending if they are a textFrame or a pathItem calls a seperate function. All seems to work well whilst I'm in the ExtendScript Toolkit environment, but when I put the script into illustrator and run it directly I get the following error. Can anyone tell me what I'm doing wrong

It seems to be refering to the code    'if (item instanceof TextFrame) {'

for (var i = doc.pageItems.length -1; i > -1; i--) {

    var item=doc.pageItems;

    if (item instanceof TextFrame) {

            changeText(item)

        }

     if (item instanceof PathItem) {

            changePath(item)

        }

    }

function changeText(item) {

    item.textRange.characterAttributes.figureStyle=FigureStyleType.TABULAR

    item.textRange.characterAttributes.fillColor=spotBlack;

    item.textRange.characterAttributes.ligature.true

    }

function changePath(item) {

    if (Math.round(item.strokeColor.cyan) == crowbarBlack.cyan &&

        Math.round(item.strokeColor.magenta)== crowbarBlack.magenta &&

        Math.round(item.strokeColor.yellow) == crowbarBlack.yellow &&

        Math.round(item.strokeColor.black) == crowbarBlack.black) {

            item.strokeColor=spotBlack;

            }

    if (Math.round(item.fillColor.cyan) == crowbarBlack.cyan &&

        Math.round(item.fillColor.magenta)== crowbarBlack.magenta &&

        Math.round(item.fillColor.yellow) == crowbarBlack.yellow &&

        Math.round(item.fillColor.black) == crowbarBlack.black) {

            item.fillColor=spotBlack;

            }

    }