Ultimate JavaScript Mastery: Control Flow

if…else

if (condition) {
 statement
}
else if (anotherCondition) {
 statement
}
else if (yetAnotherCondition) {
 statement
}
else {
}

Curley braces can be left off for only a single statement.

switch…case

let role;
switch (role) {
 case ‘guest’:
  console.log(‘Guest User’)
  break;
 case ‘moderator’:
  console.log(‘Moderator User’);
  break;
 default:
  console.log(‘Unknown User’);
}

for loop

for (init ; cond; inc) {
 statement
}

for (let i = 0; i < 5 ; i++) {
 console.log(i);
}

Just like the ‘if’ statement, Curley braces can be left off if statement is a single statement

while loop

while (cond) {
  statements
}

Equalivent to the for loop above:

let i = 0;
while (i < 5) {
  console.log(i);
  i++;
}

do... while loop

do {
  statements
} while (cond);

Equalivent to the for loop above:

let i = 0;
do {
  console.log(i);
  i++;
} while (i < 5);

for... in loop

Iterate over properties in an object

const person = {
 name: ‘James’,
 age: 19
};
for (let propertyName in person)
 console.log(propertyName, person[propertyName]);

Can be used to iterate over an array as follows:

const colors = [‘red’, ‘green’, ‘blue’];
for (let index in colors)
 console.log(index, colors[index]);

for... of loop

Iterate over elements in an array

const colors = [‘red’, ‘green’, ‘blue’];
for (let color of colors)
 console.log(color);

break and continue

Changes how the loop behaves

Use break to exit the loop:

let i = 0;
while (i <= 10) {
  if (i === 5) break; // break out of the loop when i is 5
  console.log(i);
  i++;
}

Use continue to jump to the next iteration. The following only prints odd numbers:

// Write odd numbers to the console log

let i = 0;
while (i <= 10) {
  if (i % 2) === 0) {
   i++;
   continue;
  }
  console.log(i);
  i++;
}