How to block for input in javascript

Question

Conceptually what I need to do in javascript is the following:

// A) set up stuff

// B) collect values from input
do {
    var key = readKey();
    // do stuff like loading arrays, objects, etc based on this sequential input
} while (key != '.') // period signifies completion

// C) continue to do other stuff that can only be done once the arrays and objects from before are completely loaded.

I know that IO is non-blocking in javascript. So I have tried setting keyboard listeners and looping in a setTimeout construct, but I cannot avoid program execution flying through to C) and error-ing out because all of the prerequisite processing that is part of B) is not complete.

Here is what I tried:

// A) prepare stuff
var digrams = type() // B
// C) deal with digrams (errors out if digrams not complete)

function type() {
  var loopid;

  var loop = function() {
    // NOP
  };

  document.onkeypress = function (e) {
    e = e || window.event;
    var char = String.fromCharCode(e.keyCode);
    ...
    if (char=='.') {
     document.onkeypress = null;
     clearInterval(loopid);
     return digrams; // arr of obj composed thru key input
    }
  } // keylistener

  // Start the type loop
  loopid = setInterval( loop, 10);
}   

I really need a way to work "against" javascript here. Any example code would be appreciated.

Answer 1

You can use Promise, to return a value asynchronously to .then()

// A) prepare stuff
var digrams = type();
digrams
.then(funcion handleSuccess(value) {
  // do stuff with `value` : `arr` passed to `resolve()`
}
, function handleError(err) {
  // handle error
}); // B
// C) deal with digrams (errors out if digrams not complete)

function type() {
  return new Promise(function(resolve, reject) {
    var loopid;

    var loop = function() {
      // NOP
    };

    document.onkeypress = function (e) {
      e = e || window.event;
      var char = String.fromCharCode(e.keyCode);
      ...
      if (char=='.') {
        document.onkeypress = null;
        clearInterval(loopid);
        resolve(arr);
        // return digrams; // arr of obj composed thru key input
      }
      // reject(new Error("error message"));
    } // keylistener

    // Start the type loop
    loopid = setInterval( loop, 10);
  });
}