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flow.md

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Flow

What is the output?

console.log(1);
setTimeout(function() {
  console.log(2);
}, 1000);
setTimeout(function() {
  console.log(3);
}, 0);
console.log(4);

What is the output?

function say(a) {
  alert(a);
}
say(1);
setTimeout(say(2), 5000);
setTimeout(function() {
  say(3);
}, 1000);
setTimeout(say, 2000, 4);

What's wrong? How fix?

var done = false;
$.ajax(url, function() {
  done = true;
});
while (!done) {
  someWaitingStuff();
}

Next code print 0,1,2,3,4,4,3,2,1,0 Modify only functions ( not loops ) to get output as 4,3,2,1,0,0,1,2,3,4

var a = function(i) {
  console.log(i);
};
var b = function(i) {
  console.log(i);
};
for (var i = 0; i < 5; i++) {
  a(i);
}
for (var i = 4; i >= 0; i--) {
  b(i);
}

The following recursive code will cause a stack overflow if the array list is too large. How can you fix this and still retain the recursive pattern?

var list = readHugeList();
var nextListItem = function() {
  var item = list.pop();
  if (item) {
    // process the list item...
    nextListItem();
  }
};

What is the output

(function() {
  console.log(1);
  setTimeout(() => console.log(2), 1000);
  setTimeout(() => console.log(3), 0);
  Promise.resolve(true).then(() => console.log(4));
  console.log(5);
})();

Create fetcher function, which takes url, and number of tryies to re-fetch data in case of error. You can use any load-interface ( fetch/xhr/... )

Bonus: Implement in both styles - recursion / non-recursion

What is the output

try {
  setTimeout(function() {
    throw new Error();
  }, 1000);
} catch (e) {
  alert( e);
}

Create promisify function which takes node-style (error-first) function and converts it into promise-based function. Instead of calling callback with error, data it return promise which resolves/rejectes. It worth to check if function save context for original function (this)

Create function for asyn serial list processing. Takes list and callback (element, index, list, doneCb). Returns promise wich resolved with results. Add callbacks should be called one by one.

serialProcess([1,2,3,4,5], (el, index, list, done) => {
  console.log(`${el} start`);
  setTimeout(() => {
    console.log(`${el} end`);
    done(el*el);
  }, el*100);
}).then((list) => console.log(list)); // [1,4,9,16,25]

in callback style

serialProcess(
  [1,2,3,4,5], 
  (el, index, list, done) => {
    console.log(`${el} start`);
    setTimeout(() => {
      console.log(`${el} end`);
      done(el*el);
    }, el*100);
  },
  (list) => console.log(list)
); // [1,4,9,16,25]