Run Client Script in Suitelet Available without Login

Suitelet Code

form.addButton({
  id : 'custpage_mybutton',
  label : 'MyButton',
  functionName : 'runButtonClickAction'
});
 
var fileContents = file.load(fileId).getContents();
var field = form.addField({
         id: 'custpageinjectcode',
         type: 'INLINEHTML',
         label: 'Inject Code'
       });
field.defaultValue = "<script>" + fileContents + "</script>";

Client Script code

$('custpage_mybutton').onclick = function(){ runButtonClickAction(); }
 
function runButtonClickAction(){
    alert('Button clicked');
}

Note: Following sample is a hacked version