JS Functions

Question 1

how create Function declaration?

Answer 1

For declare function we use keyword ‘functions’ functions’name, list of parameters, and functions body
function sum(a,b) {
return a+b
}
console.log(sum(2,3));
funcName start whit verb
When we call func she execute code inside the body/this is invocation/
parameters used for declare the func
arguments used for call the func
// Function declaration: starts with “function”
function isNil(value) {
return value == null;
}

Question 2

What returning value of func ‘result’?

function say(mes) {
console.log(mes);
}

let result = say(‘Hello!’)

console.log(‘Result:’, result);

Answer 2

Undefined

// function say return Hello!
// console.log(‘Result:’, result); return Result: undefined

Question 3

What is answer?

const compere = (a, b) => {
return a === b ? “equal” : a > b ? a : b;
};

console.log(compere(30, 30));

Answer 3

equal
we have func who compere the numbers

Question 4

What is answer?
const say1 = (mes) => {
return !mes ? console.log(“Don`t have massage”) : console.log(mes);
};

say1(“”);
say1(“Hello!”);

Answer 4

Don`t have massage
Hello!

Question 5

What is answer?

function add() {
let sum = 0;
for (let i = 0; i < arguments.length; i++) {
sum += arguments[i];
}
return sum;
};

console.log(add(1,2,3));

Answer 5

console.log(add(1,2,3)); //6

Question 6

Is possible to use declaration func before declare?

Answer 6

The function declaration variable is hoisted up to the top of the current scope, which means that the function can be invoked before the declaration

Question 7

Is functions are first-class citizens in JavaScript?

Answer 7

Functions are first-class citizens in JavaScript. In other words, you can treat functions like values of other types.
-Storing functions in variables
-Passing a function to another function
-Returning functions from functions

Question 8

Storing functions in variables?

function add(a,b) {
return a+ b
}
let sum = add

Answer 8

// we have two ways to execute func

console.log(add(1,2)); /3
console.log(sum(2,2)); /4

Question 9

Passing a function an argument to another function

function add(a,b) {
return a+ b
}
let sum = add

function average(a,b, fn) {
return fn(a,b)/2
}
let result1 = average(2,3, sum)

console.log(result1);

Answer 9

we use func add= sum like argument for func average
console.log(result1); 2,5

Question 10

Returning functions from functions
function compereBy(propName) {
return function (a, b) {
let x = a[propName];
let y = b[propName];
if (x > y) {
return 1;
} else if (x < y) {
return -1;
} else {
return 0;
}
};
};

let products = [
{
name:’phone’,
price:699
},
{
name:’Protector’,
price:9
},
{
name:’Memory’,
price:20
},
]
console.log(‘Prod sort by name’);
products.sort(compereBy(‘name’))
console.table(products);

console.log(‘Prod sort by price’);
products.sort(compereBy(‘price’))
console.table(products);

Answer 10

console.log(‘Prod sort by name’);
products.sort(compereBy(‘name’))

Prod sort by name
┌─────────┬─────────────┬───────┐
│ (index) │ name │ price │
├─────────┼─────────────┼───────┤
│ 0 │ ‘Memory’ │ 20 │
│ 1 │ ‘Protector’ │ 9 │
│ 2 │ ‘phone’ │ 699 │

products.sort(compereBy(‘price’))
console.table(products);

Prod sort by price
┌─────────┬─────────────┬───────┐
│ (index) │ name │ price │
├─────────┼─────────────┼───────┤
│ 0 │ ‘Protector’ │ 9 │
│ 1 │ ‘Memory’ │ 20 │
│ 2 │ ‘phone’ │ 699 │
└─────────┴─────────────┴───────┘

Question 11

/What is Anonymous func?

Answer 11

//Anonymous func is func without name
// - display message
let show = function () {
console.log(‘Anonymous func’);
}
show() //Anonymous func

Question 12

Anonymous functions as arguments. What is result?

setTimeout(() => {
console.log(‘Execute later after 1’);
},1000)

Answer 12

log - Execute later after 1 - after one sec

Question 13

What is IIFE Immediately invoked function? What is result?
(function() {
console.log(‘IIFE’);
})();

let person ={
name: ‘Lia’,
age: 23
};
(function () {
console.log(person.name +’ ‘ + ‘with age ‘ + person.age);
})(person)

Answer 13

//IIFE Immediately invoked function execution create a function and execute it immediately after the declaration
// IIFE
//Lia with age 23

Question 14

What is Arrow functions ? What is result?

let show3 = () => console.log(‘Arrow func’);
show3()

let add3 = (a,b) => console.log(a+b);
add3(5,6)

Answer 14

Arrow functions expressions that provide a shorthand for declaring anonymous functions

show3() //Arrow func

add3(5,6) //11

Question 15

What are JavaScript Callbacks?

let num = [1, 2, 3, 11, 22, 33, 44];

const isOdd = (n) => n % 2;
console.log(num.filter(isOdd));

Answer 15

Callback is a function that you pass into another function as an argument for executing later.