Statements and Declarations

Control flow

if…else

decision if

if does not executes: false, 0, “”, null, undefined, NaN:

const number = 10;

if (number < 0) console.log('less than zero'); //=> greater than zero

const number = 10;

if (number < 0) {
  console.log('less than zero'); //=> greater than zero
}

decision if

const number = 10;
let result;

if (number < 0) {
  result = 'less than zero';
}
if (number >= 0)
  result = 'equal or greater than zero';
}

console.log(result); //=> equal or greater than zero

decision if

let number = 10;
let result;

if (number < 0) {
  result = 'less than zero';
} else {
  result = 'equal or greater than zero';
}

console.log(result); //=> equal or greater than zero

decision if

const number = 10;
let result;

if (number < 0) {
  result = 'less than zero';
} else if (number > 0) {
  result = 'greater than zero';
} else {
  result = 'equal to zero';
}

console.log(result); //=> greater than zero

switch

decision switch

const number1 = 10;
const number2 = 10;
const operator = '+'; // (+, -, *, /)
let result;

// strict comparison
switch (operator) {
  case 'add':
  case '+':
    result = number1 + number2;
    break;
  case '-':
    result = number1 - number2;
    break;
  case '*':
    result = number1 * number2;
    break;
  case '/':
    result = number1 / number2;
    break;
  default:
    result = 0;
}

console.log(result); //=> 20

Iterations

while

loop while

let result = '';

while (result.length < 4) {
  result += 'x';
  console.log(result);
}
//=>
// x
// xx
// xxx
// xxxx

do…while

loop do while

let result = '';

do {
  result += 'x';
  console.log(result);
} while (result.length < 4);
//=>
// x
// xx
// xxx
// xxxx

for

loop for flag

for (let flag = 0; flag < 100; flag += 1) {
  console.log(flag);
}
//=>
// 0
// 1
// 2
// ...
// 97
// 98
// 99

let result = '';

for (let flag = 0; flag < 100; flag++) {
  result += flag < 10 ? '0' + flag : flag;
  result += flag % 10 === 9 ? '\n' : ' ';
}

console.log(result);
//=>
// 00 01 02 03 04 05 06 07 08 09
// 10 11 12 13 14 15 16 17 18 19
// 20 21 22 23 24 25 26 27 28 29
// 30 31 32 33 34 35 36 37 38 39
// 40 41 42 43 44 45 46 47 48 49
// 50 51 52 53 54 55 56 57 58 59
// 60 61 62 63 64 65 66 67 68 69
// 70 71 72 73 74 75 76 77 78 79
// 80 81 82 83 84 85 86 87 88 89
// 90 91 92 93 94 95 96 97 98 99

for…in

loop for in

Iterates over the enumerable properties of an object:

const numbers = [1, 2, 3, 4];

for (const index in numbers) {
  console.log(index);
}
//=>
// 0
// 1
// 2
// 3

const numbers = [1, 2, 3, 4];

numbers['number'] = 10;

for (let index in numbers) {
  console.log(`${index} -> ${numbers[index]}`);
}
//=>
// 0 -> 1
// 1 -> 2
// 2 -> 3
// 3 -> 4
// number -> 10

for…of

loop for of

Iterates over iterable objects (including arrays, array-like objects, iterators and generators):

const numbers = [1, 2, 3, 4];

for (let number of numbers) {
  console.log(number);
}
//=>
// 1
// 2
// 3
// 4

for…of (Array.prototype.entries())

const numbers = [1, 2, 3, 4];

numbers['number'] = 10;

for (let [index, number] of numbers.entries()) {
  console.log(`${index} => ${number}`);
}
//=>
// 0 => 1
// 1 => 2
// 2 => 3
// 3 => 4

for…of (Object.keys)

const student = {
  id: 1,
  name: 'fulano',
  email: 'fulano@gmail.com',
};

for (let index of Object.keys(student)) {
  console.log(student[index]);
}
//=>
// 1
// fulano
// fulano@gmail.com

for…of (Object.values)

const student = {
  id: 1,
  name: 'fulano',
  email: 'fulano@gmail.com',
};

for (let values of Object.values(student)) {
  console.log(values);
}
//=>
// 1
// fulano
// fulano@gmail.com

for…of (Object.entries)

const student = {
  id: 1,
  name: 'fulano',
  email: 'fulano@gmail.com',
};

for (const [key, value] of Object.entries(student)) {
  console.log(`${key} -> ${value}`);
}
//=>
// id -> 1
// name -> fulano
// email -> fulano@gmail.com

Recap

Category Statements
Control flow block, break, continue, empty, if...esle, switch, throw, try...catch
Iterations do...while, for, for...in, for...of, while, do...while
Others debugger, export, import, label
Declarations var, let, const
Functions and classes function, function*, return, class