JS Interview Questions

adv_js_prompts.js

// PROMPT ONE:

var getUserComments = function(callback) {
  // pretend this performs some async operation like an Ajax call
  var commentCount = 50;
  callback({ comments: commentCount });
};

var User = {
  fullName: 'Joe Shmoe',
  printUserInfo: function() {
    getUserComments(function(data) {
      console.log(this.fullName + ' made ' + data.comments + ' comments');
    });
  }
};

User.printUserInfo();

/* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */

// PROMPT TWO:

var theFinalCountDown = [1, 2, 3, 4, 5];

for (var i = 0; i < theFinalCountDown.length; i++) {
   var count = theFinalCountDown[i];
   setTimeout(function() { console.log(count); }, 1000);        
}

/* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */

// PROMPT THREE (Non-React):

console.log("Hi!")

setTimeout(function() {
  console.log('Hello!')
}, 0)

console.log("Hola!")

// In what order do these return?
// What is going on here?

// PROMPT THREE (React):

this.setState({ canView: true }, () => { console.log("Hello!") })

// In what order would these operations happen?
// Why would you want to set a callback in the setState instead of running the console log immediately afterwards?

/* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */

// PROMPT FOUR:

function runMultipleQueries(queries) {
 var results = [];
 queries.forEach(doQuery);

 return results;

 function doQuery(query) {
   findData(query)
   .then(results.push.bind(results));
 } 
}

console.log(runMultipleQueries([queryA, queryB, queryC]))

// Assume findData exists and returns a promise and each of these query variables are defined. What would this output if you ran the last line?
// How would you get this to log all the results in sequence (in the order they were passed, queryA, queryB and so on)?

/* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */