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Control flow statements help determine the order in which different parts of your code run. In JavaScript, you have if/else statements, switch/case statements, and various types of loops. They work similarly to Java’s control flow constructs.
1. If/Else Statements
These statements let you execute different blocks of code based on a condition. This is similar to Java’s if/else statements.
Syntax:
if (condition) {
// code to execute if condition is true
} else {
// code to execute if condition is false
}
Example Program:
let x = 5;
if (x > 2) {
console.log("x is greater than 2");
} else {
console.log("x is less than or equal to 2");
}
Output:
x is greater than 2
Comparison to Java:
This is very similar to Java’s if statements:
int x = 5;
if (x > 2) {
System.out.println("x is greater than 2");
} else {
System.out.println("x is less than or equal to 2");
}
2. Switch/Case Statements
These are used to select one block of code to execute based on the value of an expression. It’s similar to Java’s switch statements.
Syntax:
switch (expression) {
case value1:
// code to execute if expression equals value1
break;
case value2:
// code to execute if expression equals value2
break;
default:
// code to execute if no cases match
}
Example Program:
let day = "Monday";
switch (day) {
case "Monday":
console.log("Today is Monday");
break;
case "Tuesday":
console.log("Today is Tuesday");
break;
default:
console.log("Today is neither Monday nor Tuesday");
}
Output:
Today is Monday
Comparison to Java:
This is similar to Java’s switch statement:
String day = "Monday";
switch (day) {
case "Monday":
System.out.println("Today is Monday");
break;
case "Tuesday":
System.out.println("Today is Tuesday");
break;
default:
System.out.println("Today is neither Monday nor Tuesday");
}
3. Loops
Loops let you repeat a block of code multiple times. JavaScript has for, while, and do/while loops, just like Java.
a. For Loop
Use this when you know how many times you need to loop.
Syntax:
for (initialization; condition; increment/decrement) {
// code to execute in each iteration
}
Example Program:
for (let i = 1; i <= 5; i++) {
console.log(i);
}
Output:
1
2
3
4
5
Comparison to Java:
Similar to Java’s for loop:
for (int i = 1; i <= 5; i++) {
System.out.println(i);
}
b. While Loop
Use this when you don’t know how many times you need to loop but have a condition.
Syntax:
while (condition) {
// code to execute in each iteration
}
Example Program:
let i = 1;
while (i <= 5) {
console.log(i);
i++;
}
Output:
1
2
3
4
5
Comparison to Java:
Similar to Java’s while loop:
int i = 1;
while (i <= 5) {
System.out.println(i);
i++;
}
c. Do/While Loop
This loop executes the block of code at least once, even if the condition is false.
Syntax:
do {
// code to execute in each iteration
} while (condition);
Example Program:
let i = 1;
do {
console.log(i);
i++;
} while (i <= 5);
Output:
1
2
3
4
5
Comparison to Java:
Similar to Java’s do/while loop:
int i = 1;
do {
System.out.println(i);
i++;
} while (i <= 5);
Control flow statements are essential for making decisions and repeating actions in your programs. By understanding and using these statements effectively, you can create more complex and dynamic JavaScript programs.