In this chapter, we will learn about JavaScript control flow statements. These statements are used to control the execution of code based on certain conditions and loops. We will cover:
ifStatementelseStatementelse ifStatementswitchStatementforLoopwhileLoopdo...whileLoopbreakStatementcontinueStatement
if Statement
The if statement is used to execute a block of code if a specified condition is true.
Syntax
if (condition) { // code to be executed if the condition is true } Example
let age = 18; if (age >= 18) { console.log("You are an adult."); } // Output: You are an adult. else Statement
The else statement is used to execute a block of code if the if condition is false.
Syntax
if (condition) { // code to be executed if the condition is true } else { // code to be executed if the condition is false } Example
let age = 16; if (age >= 18) { console.log("You are an adult."); } else { console.log("You are a minor."); } // Output: You are a minor. else if Statement
The else if statement is used to specify a new condition to test if the first condition is false.
Syntax
if (condition1) { // code to be executed if condition1 is true } else if (condition2) { // code to be executed if condition1 is false and condition2 is true } else { // code to be executed if condition1 and condition2 are false } Example
let marks = 75; if (marks >= 90) { console.log("Grade: A"); } else if (marks >= 80) { console.log("Grade: B"); } else if (marks >= 70) { console.log("Grade: C"); } else { console.log("Grade: D"); } // Output: Grade: C switch Statement
The switch statement is used to execute one of many blocks of code based on the value of an expression.
Syntax
switch (expression) { case value1: // code to be executed if expression === value1 break; case value2: // code to be executed if expression === value2 break; // add more cases as needed default: // code to be executed if expression doesn't match any case } Example
let day = 2; switch (day) { case 1: console.log("Monday"); break; case 2: console.log("Tuesday"); break; case 3: console.log("Wednesday"); break; default: console.log("Another day"); } // Output: Tuesday for Loop
The for loop is used to execute a block of code a specified number of times.
Syntax
for (initialization; condition; increment) { // code to be executed } Example
for (let i = 0; i < 5; i++) { console.log(i); } // Output: 0 1 2 3 4 while Loop
The while loop is used to execute a block of code as long as a specified condition is true.
Syntax
while (condition) { // code to be executed } Example
let i = 0; while (i < 5) { console.log(i); i++; } // Output: 0 1 2 3 4 do…while Loop
The do...while loop is similar to the while loop, but it executes the block of code at least once before checking the condition.
Syntax
do { // code to be executed } while (condition); Example
let i = 0; do { console.log(i); i++; } while (i < 5); // Output: 0 1 2 3 4 break Statement
The break statement is used to exit a loop or switch statement before it completes its execution.
Example
for (let i = 0; i < 10; i++) { if (i === 5) { break; } console.log(i); } // Output: 0 1 2 3 4 continue Statement
The continue statement is used to skip the current iteration of a loop and continue with the next iteration.
Example
for (let i = 0; i < 10; i++) { if (i === 5) { continue; } console.log(i); } // Output: 0 1 2 3 4 6 7 8 9 Conclusion
In this chapter, you learned about JavaScript control flow statements, including if, else, else if, switch, for loop, while loop, do...while loop, break, and continue statements. These control flow statements are essential for making decisions and repeating tasks in your code.