var layer = activeDocument.layers[0];
if (layer.kind == 'LayerKind.TEXT') {
for (var i=1; i < 50; i++) {
layer.textItem.contents = i.toString();
var saveFile = File('/C/' + i + '.png');
sfwPNG24(saveFile);
}
};


function sfwPNG24(saveFile){
var pngOpts = new ExportOptionsSaveForWeb();
pngOpts.format = SaveDocumentType.PNG;
pngOpts.PNG8 = false;
pngOpts.transparency = true;
pngOpts.interlaced = false;
pngOpts.quality = 100;
activeDocument.exportDocument(new File(saveFile),ExportType.SAVEFORWEB,pngOpts);
}