knex select() returns before completing query in javascript

Question

I have a function like this:

function get_projects() {
    var project_names=[];
    knex('projects').select('name').then(function (a) { 
        project_names.push(a);
    })
    return project_names;
}

This function executes the return statement return project_names; before completing project_names.push(a) statement and what I get after calling this function is an empty array, even though my db has results (I can see this if i log within the function a())

Answer 1

knex select() returns a promise so that you can continue the flow within then() function.

knex('projects').select('name').then(function(projectNames){
    //do something here
    console.log(projectNames);
});

Answer 2

Nodejs is asynchronous, so as soon as your line knex('projects').select('name').then... is executed, the line `return project_names;' is run. As you have found out, it didn't wait until it was filled with values!

The standard "return" at the end of the methods isn't a good programming style for Nodejs, which is event based. It has its place, but more common is a callback approach. Consider reading some tutorials on this new approach (I like this one)

You might change your current code to something like:

function print_project_names() {
  get_projects( function(names){
    for( var i = 0; i < names.length; i++ )
    {
      console.log(names[i]+'\n');
    } 
  });
}

function get_projects( callback ) {
  var project_names=[];
  knex('projects').select('name').then(function (a) { 
     project_names.push(a);
     callback(project_names);
  })
}

NOTE: This is not optimized code

Here, when you want to print the project names (unsure your real goal), you are passing an actual function definition, as the "callback", into "get_projects". As the events fire, once the results are pushed into the project names, the callback is called with your new list.