Wait for user input in node.js

I just want to mention that I tried a bunch of techniques from blogs for getting user input but the examples were always in the context of a program that only asks for user input... and they always work but there's never any problem of node.js continuing on to the next lines of code because there are none.

I have to get user input and then verify that the input is valid so I created this construct:

while ( designAppealTest(subject) == false ) {
            subject[DESIGN_APPEAL] = ei.errorInput('designAppeal for the subject', iteration, subject[DESIGN_APPEAL])
        }

The function that it calls is this:

module.exports.errorInput =  function (fieldName, iteration, originalValue) {
    originalValue = originalValue || 'false'
    console.log('\n\n' + fieldName + ' for the subject' + ' contains an invalid value in for #' + i)

    if (originalValue !== false)
        console.log('original value of field = ' + originalValue)

    console.log('\nPlease enter a new value for it:\n')

    process.stdin.on('data', function (text) {
        console.log('received data:', text);
        return text;
    });

}

This works except that it keeps going through the while loop before the user has a chance to input a value. So all I see is the prompt asking the user to input a value 40,000 times a second. How can I make node.js wait until a value is entered before continuing the loop? Is the construct itself wrong or is it because I'm not halting it from being asynchronous?

CFrei:

Okay I added a callback to check() itself as well:

checkedSubject = check(subject, function(v) {
            return v;
        });

        console.log('checkedSubject = ' + checkedSubject)

        function check(listing, callback) {
            if (designAppealTest(subject) == false ) {
                ei.errorInput('designAppeal', iteration, listing[DESIGN_APPEAL], function(v) {
                    listing[DESIGN_APPEAL] = v;
                    check(listing)
                    });
            } else {
                callback(listing);
            }
        }

I'm still getting the same problem - it will ask for input but execute everything after it immediately.

That's just how node.js works, it is designed around asynchronous, non-blocking I/O for high concurrency. If you need help organizing control flow because of how node.js works, you might look into using a module such as async.

Well, the async approach is about "never coming back" to any return value, just give the next callback to the function. Your "loop" should look like that:

function check() {
    if (designAppealTest(subject) == false ) {
            ei.errorInput('designAppeal for the subject', iteration, subject[DESIGN_APPEAL], function(v) { subject[DESIGN_APPEAL] = v; check() })
    }
}

(Please note the recursive call to simulate your "while".)

And instead of

return text;

you call that function (lets name it cb):

cb(text)

And yes, libs like async or Promise-Library help to make that look all a bit nicer.