js conditions

Conditional Statements in JavaScript

1. If Statement

The if statement executes a block of code only if a specified condition is true.

Example 1: Display "Good morning" if time is less than 10

var d = new Date();
var time = d.getHours();

if (time < 10) {
    document.write("<b>Good morning</b>");
}
Example 2

// Display "Lunch-time!" if the time is 11
var time = new Date().getHours();
if (time == 11) {
    document.write("<b>Lunch-time!</b>");
}

    Note: When comparing variables, always use == (double equals) instead of a single equals sign (=).

2. if...else Statement

If a condition is true, one block of code will run. If it is false, another block of code will execute.
Syntax

if (condition) {
    // Code to be executed if the condition is true
} else {
    // Code to be executed if the condition is false
}

Example

var time = new Date().getHours();
if (time < 10) {
    document.write("Good morning!");
} else {
    document.write("Good day!");
}

3. if...else if...else Statement

Use this when you want to check multiple conditions.
Syntax

if (condition1) {
    // Executes if condition1 is true
} else if (condition2) {
    // Executes if condition2 is true
} else {
    // Executes if none of the conditions are true
}

Example

var time = new Date().getHours();
if (time < 10) {
    document.write("<b>Good morning</b>");
} else if (time > 10 && time < 16) {
    document.write("<b>Good day</b>");
} else {
    document.write("<b>Hello World!</b>");
}

The switch Statement

Use the switch statement to select one of many code blocks to execute.
Syntax

switch (expression) {
    case value1:
        // Code block 1
        break;
    case value2:
        // Code block 2
        break;
    default:
        // Code to execute if no match is found
}

Example

var day = new Date().getDay();
switch (day) {
    case 5:
        document.write("Finally Friday");
        break;
    case 6:
        document.write("Super Saturday");
        break;
    case 0:
        document.write("Sleepy Sunday");
        break;
    default:
        document.write("I'm looking forward to this weekend!");
}

Loops in JavaScript
1. for Loop

Use a for loop when you know how many times the loop should run.
Syntax

for (var i = startValue; i <= endValue; i++) {
    // Code to execute in each iteration
}

Example

for (var i = 0; i <= 10; i++) {
    document.write("The number is " + i + "<br>");
}

Output:

The number is 0  
The number is 1  
The number is 2  
...
The number is 10  

2. while Loop

Use a while loop when you don't know how many times it should run beforehand.
Syntax

while (condition) {
    // Code to be executed
}

Example

var i = 0;
while (i <= 10) {
    document.write("The number is " + i + "<br>");
    i++;
}

3. do...while Loop

This loop always runs at least once, even if the condition is false.
Syntax

do {
    // Code to be executed
} while (condition);

Example

var i = 0;
do {
    document.write("The number is " + i + "<br>");
    i++;
} while (i < 0);

Output:

The number is 0  

    Even though the condition i < 0 is false, the loop executes once before checking the condition.

Break & Continue Statements
1. break Statement

Exits a loop immediately when a specific condition is met.
Example

for (var i = 0; i <= 10; i++) {
    if (i == 3) {
        break;
    }
    document.write("The number is " + i + "<br>");
}

Output:

The number is 0  
The number is 1  
The number is 2  

    The loop stops at 3 because of break.

2. continue Statement

Skips the rest of the loop iteration and jumps to the next iteration.
Example

for (var i = 0; i <= 10; i++) {
    if (i == 3) {
        continue;
    }
    document.write("The number is " + i + "<br>");
}

Output:

The number is 0  
The number is 1  
The number is 2  
The number is 4  
...
The number is 10  

    The number 3 is skipped because of continue.

Conclusion

This guide covered conditional statements (if, else, switch), loops (for, while, do...while), and loop control (break, continue) in JavaScript. These concepts are fundamental for controlling program flow efficiently. 🚀