Button onClick, not functioning

good to know. Here is the complete working code

#target 'photoshop'

//Array 
	var languages = ['en','tr','sv','da','nb','ru','ja','zh-hant','zh-hans','pt-br','ko','it','fr','de','es'];

//Reference to the document
	var doc = app.activeDocument;
	
//Counter for progress
	var counter = 0;
	
//*************************************************************************
//Create the GUI window
	var appWindow = new Window('dialog', 'CRM Exporter');
//Styling the window
	//Size (must use an window.onShow(){}; callback
	appWindow.onShow = function(){appWindow.size = 'width: 230, height: 230';}
//The Create Directory input
	var createDir = appWindow.add('statictext',undefined,'Create Folder Name:');
//Input textfield
	var dirNameInpt = appWindow.add('edittext',undefined,undefined);
	dirNameInpt.characters = 20;
	dirNameInpt.active = true;
//Progress bar
    var numFiles = languages.length;
    var progBar = appWindow.add('statictext',undefined, 'Progress:');
    var progFiles = appWindow.add('statictext',undefined, counter + ' of ' + numFiles + ' ');
//The execute button
	var execBtn = appWindow.add('button',undefined,'Export');
//On execute button press
	execBtn.onClick = function()
	{
		
	//Loop through the language groups, making each one visible and exporting 
	//and then hiding the group in turn
		for(var i=0; i<doc.layerSets.length; i++)
		{
			//Temp current layer
			var currentLayer = doc.layerSets[i];
			
			//File name uses the language abbreviations from the languages list as file name
			var fileName = languages[i];
			
			//Step 1. make the current group visible
			currentLayer.visible = true;
			
			//Step 2. export the image as PNG
			exPNG24(fileName, dirNameInpt.text);
			
			//Step 3. make the current group invisible
			currentLayer.visible = false;
			
			//Update the counter
          counter++;
          progFiles.text = counter + ' of ' + numFiles + ' ';
		}
		
		//Close after completeing the loop
		appWindow.close();
	
	};
//Close button
    var closeBtn = appWindow.add('button',undefined,'Close');
    closeBtn.onClick = function()
    {
        appWindow.close();
    };
//Display the GUI
	appWindow.show();
//*************************************************************************

//Functions

function exPNG24(n, d)
    {
		var name = n;
		var directory = d;
		
       //Create a new directory and file name
       var folder = new Folder(doc.path + '/' + directory);
	   //If the directory doesn't currently exist then create it
		if(!folder.exists){
			folder.create();
		}

        var file = new File(folder + '/' + name + '.png');
        
        var options = new ExportOptionsSaveForWeb();
        
        options.format = SaveDocumentType.PNG;
        //Use PNG-24
        options.PNG8 = false;
        //Preserve transparency
        options.transparency = true;
        options.interlaced = false;
        options.embedColorProfile = false;
        //Maximum quality and medium compression to keep file size low
        options.quality = 100;
        options.compression = 5;
        
        //export the image
       doc.exportDocument(file, ExportType.SAVEFORWEB, options);
            
    }