timer.js

for (var i = 0; i < 3; i++) { 
    setTimeout(() => console.log(i), 1);
  }
  
  // In what order will the numbers 1-4 be logged to the console when the code below is executed? Why?
(function() {
    console.log(1); 
    setTimeout(function(){console.log(2)}, 1000); 
    setTimeout(function(){console.log(3)}, 0); 
    console.log(4);
})();

function doAsyncTask(cb) {

  setTimeout(() => {
  
  console.log("Async Task Calling Callback");
  
  cb();
  
  },
  
  1000);
  
  }
  
  doAsyncTask(() => console.log("Callback Called"));

  
    
    // o/p-
    // Async Task Calling Callback
    // Callback Called
  
// What is logged?

// it logs 5 five times since settimeout runs the log function after for loop is done.
// settimeout is an async process.

let i;
for (i = 0; i < 5; i++) {
  const log = () => {
    console.log(i); // 5  5 times
  };
  setTimeout(log, 100);
}

for (var g = 0; g < 5; g++) {
  setTimeout(function () {
    console.log(g, 'g');
  }, 100);
}

// 5
// 5
// 5
// 5
// 5
// we can resolve this problem by passing i in the log method.

let j;
for (j = 0; j < 5; j++) {
  const log = (i) => {
    console.log(j);
  };
  setTimeout(log, 100, j);
}

// example
console.log('one');
setTimeout(function () {
  // this function will run in end after promise
  console.log('two');
}, 0);
Promise.resolve().then(function () {
  console.log('three');
});
console.log('four');

// one
// four
// three
// two

// example
var obj = {
  id: 'awesome',
  cool: function coolFn() {
    console.log(this.id);
  },
};

var id = 'not awesome';

obj.cool(); // awesome

// problem
setTimeout(obj.cool, 100); // undefined

// solution?

// const arr = [10, 12, 15, 21];
// for (var k = 0; k < arr.length; k++) {
//   setTimeout(function() {
//     console.log('Index: ' + k + ', element: ' + arr[k]);
//   }, 1000);
// } // log 4 five times

// Closures can be used to prevent this problem by creating a unique scope for each iteration,
// storing each unique value of the variable within its scope, as follows:

// const arr = [10, 12, 15, 21];
// for (var l = 0; l < arr.length; l++) {
//   // pass in the variable i so that each function
//   // has access to the correct index
//   setTimeout(function(i_local) {
//     return function() {
//       console.log('The index of this number is: ' + i_local);
//     }
//   }(l), 1000);
// } // log 0, 1, 2, 3

// Another way to solve the above issue is by using let keyword

const arr = [10, 12, 15, 21];
for (let a = 0; a < arr.length; a++) {
  setTimeout(function () {
    console.log('The index of this number is: ' + a);
  }, 3000);
}

// Write a function that will loop through a list of integers and print the index of each element after a 3-second delay.

for (var b = 0; b < 3; b++) {
  setTimeout(
    (function (il) {
      return function () {
        console.log(il);
      };
    })(b),
    1000 + b
  );
}

for (var c = 0; c < 5; c++) {
  setTimeout(function () {
    console.log(c, 'c');
  }, c * 1000);
}

for (var d = 0; d < 5; d++) {
  (function (d) {
    setTimeout(function () {
      console.log(d, 'd');
    }, d * 1000);
  })(i);
}

for (var e = 0; e < 10; e++) {
  setTimeout(console.log.bind(console, e, 'e'), 10);
}

for (var f = 0; f < 3; f++) {
  setTimeout(function log() {
    console.log(f, 'f');
  }, 1000);
}

// example
function doAsyncTask(cb) {
  setTimeout(
    () => {
      console.log('Async Task Calling Callback');

      cb();
    },

    1000
  );
}

doAsyncTask(() => console.log('Callback Called'));

// example
setTimeout(function cb1() {
  console.log('cb1');
}, 5000);

let p1 = new Promise((resolve, reject) => {
  resolve('foo');
});
let p2 = new Promise((resolve, reject) => {
  reject('bar');
});
console.log('bip');
p1.then((val) => {
  console.log(val);
  return p2;
})
  .then((val) => {
    console.log('baz');
  })
  .catch((err) => {
    console.log(err);
  });
console.log('bop');

// bip
// bop
// foo
// bar

setTimeout(function () {
  console.log('Welcome to system design after 2 seconds');
}, 2000);

var deliEmployeeName = 'Alex';
var customerName = 'Bailey';
setTimeout(function greetTheCustomer() {
  console.log(
    'Hello' +
      customerName +
      ' my name is' +
      deliEmployeeName +
      'What can I get you today?'
  );
}, 100);

var timesRun = 0;
var interval = setInterval(function () {
  timesRun += 1;
  if (timesRun === 4) {
    clearInterval(interval);
  }
  console.log('timer');
}, 100);