Control Flow

The basic notation of control flow in JS involves () for any logical condition/expression and {} to indicate what to do for that logic. Examples are given below.

1. if, else if, else

if (condition || alternativeCondition) {
  // code to execute if condition is true
} else if (otherCondition && otherCondition2) {
  // code to execute if otherCondition is true
} else {
  // code to execute if none of the conditions are true
}

2. switch

Remember that in the beginning { is used for separation. However, for cases, we use :. The values refer to the value of expression. If none of them are satisfied, default is performed.

switch (expression) {
  case value1:
    // code to execute if expression === value1
    break;
  case value2:
    // code to execute if expression === value2
    break;
  default:
    // code to execute if expression doesn't match any case
}

3. for loop

for (initialization; condition; update) {
  // code to execute repeatedly while condition is true
}
 
for (let i = 0; i < 5; i++) {
    console.log("Iteration:", i);
}
 
// Output:
// Iteration: 0
// Iteration: 1
// Iteration: 2
// Iteration: 3
// Iteration: 4
 

4. while loop

while (condition) {
  // code to execute repeatedly while condition is true
}

5. do…while Loop

do {
  // code to execute at least once, and repeatedly while condition is true
} while (condition);
 

6. for…of Loop - This is commonly used with basic iterable data structures such as Arrays, strings, sets, maps, etc.

for (const element of iterable) {
  // code to execute for each element in the iterable
}
 
const colors = ["red", "green", "blue"];
for (const color of colors) {
    console.log(color);
}
 
// Output:
// red
// green
// blue
 

7. for…in Loop - This is commonly used for Objects (including arrays, but generally used for object properties)

for (const key in object) {
  // code to execute for each key
}
 
const person = { name: "Alice", age: 30 };
for (const key in person) {
    console.log(key, ":", person[key]);
}
 
// Output:
// name : Alice
// age : 30
 

8. .forEach() method - This method is used to execute a provided function once for each element in an array. Also, it is commonly used with arrow functions.

const numbers = [1, 2, 3, 4];
 
numbers.forEach((number) => {
  console.log(number * 2); // Output: 2, 4, 6, 8
});

1. break and continue

• break: Exits the loop or switch statement immediately.
• continue: Skips the current iteration and proceeds to the next iteration of the loop.

for (let i = 0; i < 10; i++) {
  if (i === 5) {
    break; // exits the loop when i is 5
  }
  if (i % 2 === 0) {
    continue; // skips the current iteration if i is even
  }
  console.log(i); // prints odd numbers less than 5
}