Ad. Javascript.info part 4

Question 1

In a browser it is named _______for Node.js it is ______, for other environments it may have another name.

Answer 1

“window”,

“global”

Question 2

alert(“Hello”);

// the same as
\_\_\_\_\_\_\_\_\_alert("Hello");

Answer 2

window.

Question 3

Open Google using alert

Answer 3

window.open(‘http://google.com’);

Question 4

shows the browser window height with alert

Answer 4

alert(window.innerHeight); //

Question 5

Top-level_______ variables and _________automatically become properties of window.

Answer 5

var

Function decelerations

Question 6

var x = 5;

alert(window.x); //

window.x = 0;

alert(x); //

Answer 6

5 (var x becomes a property of window)

0, variable modified

Question 7

let x = 5;

alert(window.x);

Answer 7

undefined

Question 8

the value of “this” in the global scope is ______.

Answer 8

window

Question 9

As of now, the multi-purpose window is considered a design mistake in the language to avoid this Javascript has a built in ______

Answer 9

modules.

Question 10

fix script below so x becomes “undefined”.

var x = 5;

alert(window.x);

Answer 10

let x = 5;

alert(window.x); // undefined

Question 11

let x = 5;

alert(x); //

Answer 11

5

Question 12

alert(this); //

Answer 12

undefined

Question 13

Using global variables is generally discouraged.

TRUE / FALSE

Answer 13

TRUE

Question 14

There should be as few global variables as possible, but if we need to make something globally visible, we may want to put it into________ or _______

Answer 14

window

global

Question 15

As we already know, functions in JavaScript are_____.

Every value in JavaScript has a type. What type is a function?

In JavaScript, functions are _________

Answer 15

values

objects

Question 16

function sayHi() {
  alert("Hi");
}

alert(sayHi.name); //

Answer 16

sayHi

Question 17

function sayHi() {
  alert("Hi");
}

alert(__________); // sayHi

Answer 17

sayHi.name

Question 18

WRITE AS A FUNCTION DECLEARATION

let sayHi = function() {
  alert("Hi");
}

Answer 18

function sayHi() {
  alert("Hi");
}

Question 19

function f2(a, b) {}

alert(f2.length); //

Answer 19

2

Question 20

function many(a, b, ...more) {}
alert(many.length); //

Answer 20

2

Question 21

A property is a variable

TRUE / FALSE

Answer 21

FALSE

A property is not a variable

Question 22

function sayHi() {
  alert("Hi");
  sayHi.counter++;
}
sayHi.counter = 0; 

sayHi(); // Hi
sayHi(); // Hi

console.log(sayHi.counter);

Answer 22

2

Question 23

sayHi.counter is or is not a variable in the function sayHi()

function sayHi() {
  alert("Hi");

  // let's count how many times we run
  sayHi.counter++;
}
sayHi.counter = 0;

Answer 23

IS NOT

Question 24

What are the two special things about the name function?

Answer 24

1. It allows the function to reference itself internally.

2. It is not visible outside of the function.

Question 25

let sayHi = function func(who) {
  if (who) {
    alert(`Hello, ${who}`);
  } else {
    func("Guest"); // use func to re-call itself
  }
};

func(); //

Answer 25

// But this won't work:
func not defined

Question 26

let sayHi = function func(who) {
  if (who) {
    alert(`Hello, ${who}`);
  } else {
    func("Guest"); // use func to re-call itself
  }
};

sayHi(); //

Answer 26

Hello, Guest

Question 27

WHATS THE ISSUE WITH THIS CODE?

let sayHi = function(who) {
  if (who) {
    alert(`Hello, ${who}`);
  } else {
    sayHi("Guest");
  }
};

Answer 27

The problem with that code is that the value of sayHi may change. The function may go to another variable, and the code will start to give errors:

we use Named Function Expression to avoid the above.

Question 28

let sayHi = function(who) {
  if (who) {
    alert(`Hello, ${who}`);
  } else {
    sayHi("Guest"); 
  }
};

let welcome = sayHi;
sayHi = null;

welcome(); //

Answer 28

Error: sayHi is not a function

Question 29

let sayHi = function func(who) {
  if (who) {
    alert(`Hello, ${who}`);
  } else {
    func("Guest"); 
  }
};

let welcome = sayHi;
sayHi = null;

welcome(); // returns and why

Answer 29

welcome guest

Now it works, because the name “func” is function-local.

Question 30

the __________ allows to turn any string into a function. For example, we can receive a new function from a server and then execute it:

Answer 30

new Function

Question 31

a function remembers where it was born in the special property __________

Answer 31

[[Environment]].

Question 32

when a function is created using new Function, its [[Environment]] references not the current________ Environment, but instead the________

Answer 32

Lexical

global one.

Question 33

___________ allows to run a function once after the interval of time.

Answer 33

setTimeout

Question 34

_________ allows to run a function regularly with the interval between the runs.

Answer 34

setInterval

Question 35

We may decide to execute a function not right now, but at a certain time later. That’s called _________

Answer 35

“scheduling a call”.

Question 36

The delay before run, in milliseconds (_______ ms = 1 second), by default 0.

Answer 36

1000

Question 37

the code runs after how much time?

function sayHi() {
  alert('Hello');
}

setTimeout(sayHi, 1000);

Answer 37

1 second

1000ms = 1 second

Question 38

setTimeout(“alert(‘Hello’)”, 5000);

what happens?

Answer 38

alert “hello” after 5 seconds

Question 39

pass setTimeout with sayHi, 1000

Answer 39

setTimeout(sayHi, 1000);

dont use () next to sayHi

Question 40

A call to setTimeout returns a “timer identifier”__________ that we can use to cancel the execution

Answer 40

timerId

Question 41

The setInterval method has the same syntax as setTimeout:

TRUE / FALSE

Answer 41

TRUE

Question 42

All arguments have the same meaning. But unlike _________ it runs the function not only once, but regularly after the given interval of time.

Answer 42

setTimeout

Question 43

To stop further calls, we should call _____________

Answer 43

clearInterval(timerId).

Question 44

Time goes on while alert is shown

TRUE / FALSE

Answer 44

true

Question 45

There are two ways of running something regularly.

Answer 45

1. setInterval

2. recursive setTimeout

Question 46

What guarantees a delay between the executions?

Answer 46

Recursive setTimeout guarantees a delay between the executions, setInterval – does not.

Question 47

The recursive________ guarantees the fixed delay

Answer 47

setTimeout

Question 48

setTimeout(expression, timeout);

Answer 48

runs the code/function once after the timeout.

Question 49

runs the code/function once after the timeout.

Answer 49

setTimeout(expression, timeout);

Question 50

setInterval(expression, timeout);

Answer 50

runs the code/function in intervals, with the length of the timeout between them.

Question 51

runs the code/function in intervals, with the length of the timeout between them.

Answer 51

setInterval(expression, timeout);

Question 52

__________(function () {
something();
}, 1000); // Execute something() 1 second later.

Answer 52

setTimeout

Question 53

___________function () {
somethingElse();
}, 2000); // Execute somethingElse() every 2 seconds.

Answer 53

setInterval

Question 54

_________ should not be nested into its callback function by the script author to make it loop, since it loops by default. It will keep firing at the interval unless you call clearInterval().

Answer 54

setInterval

Question 55

if you want to loop code for animations or clocks Then use _________ setInterval or setTimeout

Answer 55

setInterval.