how to call following node.js function in spread.js?

The following code is written in server.js file which is nodejs code

  app.get("/api/todos",function(req, res){
   todo.find(function(error, todos){
    if(error)
     res.send(error);

     res.json(todos);
   });        
 });

Now I want to call that into my spreadTest.js which is using spread.js, how do I do that?

I'm assuming that your spreadTest.js file is running client side (in a browser) since spread.js is a toolkit for spreadsheets. That means that you will need to send an HTTP GET request to the server running node/server.js. You can create a function in spreadTest.js that performs the request like this:

// Returns JSON object
function getTodos()
      {
           var url = YOUR-WEBSITE + "/api/todos";
           var xmlHttp = new XMLHttpRequest();
           xmlHttp.open("GET", url, true);
           xmlHttp.send(null);
           return xmlHttp.responseText;
      }