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Explain the if…else statement in JavaScript?
The if…else statement in JavaScript is a conditional statement that is used to execute code based on a condition. The if…else statement has the following syntax:
if (condition) {
// code to be executed if condition is true
} else {
// code to be executed if condition is false
}
The condition is a Boolean expression that evaluates to either true or false. If the condition evaluates to true, the code inside the if block is executed. If the condition evaluates to false, the code inside the else block is executed.
For example, the following code uses an if…else statement to check if the value of the variable num is greater than 10:
const num = 10;
if (num > 10) {
console.log("The value of num is greater than 10");
} else {
console.log("The value of num is not greater than 10");
}
If the value of num is greater than 10, the code inside the if block will be executed. If the value of num is not greater than 10, the code inside the else block will be executed.
The if...else statement can be used to execute different code depending on the value of a variable or expression. It is a very powerful tool that can be used to control the flow of your code.
Here are some rules to follow when using the if…else statement:
The
conditionmust be a Boolean expression.The
ifblock and theelseblock must be terminated by a semicolon.The
ifblock and theelseblock can contain any valid JavaScript code.
How to use the switch statement in JavaScript?
The switch statement in JavaScript is a conditional statement that is used to execute code based on the value of a variable or expression. The switch statement has the following syntax:
switch (expression) {
case value1:
// code to be executed if expression is equal to value1
break;
case value2:
// code to be executed if expression is equal to value2
break;
default:
// code to be executed if expression is not equal to any of the values
}
The expression is a variable or expression that is evaluated. The value of the expression is then compared to the values in the case statements. If the value of the expression is equal to the value of a case statement, the code inside the case statement is executed. The break statement is used to exit the switch statement. If the value of the expression is not equal to any of the values in the case statements, the code inside the default block is executed.
For example, the following code uses a switch statement to check the value of the variable color:
const color = "red";
switch (color) {
case "red":
console.log("The color is red");
break;
case "green":
console.log("The color is green");
break;
case "blue":
console.log("The color is blue");
break;
default:
console.log("The color is not red, green, or blue");
}
If the value of color is equal to “red”, the code inside the case statement with the value “red” is executed. If the value of color is equal to “green”, the code inside the case statement with the value “green” is executed. If the value of color is equal to “blue”, the code inside the case statement with the value “blue” is executed. If the value of color is not equal to any of the values in the case statements, the code inside the default block is executed.
The switch statement can be used to execute different code depending on the value of a variable or expression. It is a very powerful tool that can be used to control the flow of your code.
Here are some rules to follow when using the switch statement:
The
expressionmust be a variable or expression that can be evaluated to a value.The
casestatements must be terminated by a semicolon.The
breakstatement is optional, but it is a good practice to use it to exit the switch statement.The
defaultblock is optional, but it is a good practice to include it in case the value of the expression does not match any of thecasestatements.
Provide examples of using the ternary operator as a shorthand for an if…else statement?
The ternary operator in JavaScript is a shorthand for an if…else statement. The ternary operator has the following syntax:
condition ? value_if_true : value_if_false;
The condition is a Boolean expression that evaluates to either true or false. If the condition evaluates to true, the value of the value_if_true expression is returned. If the condition evaluates to false, the value of the value_if_false expression is returned.
For example, the following code uses the ternary operator to check if the value of the variable num is greater than 10:
const num = 10;
const result = num > 10 ? "greater than 10" : "less than or equal to 10";
console.log(result); // "less than or equal to 10"
If the value of num is greater than 10, the value of the value_if_true expression, which is “greater than 10”, is returned. If the value of num is not greater than 10, the value of the value_if_false expression, which is “less than or equal to 10”, is returned.
The ternary operator can be used to replace an if…else statement in many cases. It is a shorter and more concise way of writing code.
Here are some other examples of using the ternary operator:
// Check if a number is even
const num = 10;
const isEven = num % 2 === 0 ? true : false;
// Display a message based on the value of a variable
const age = 18;
const message = age >= 18 ? "You are an adult" : "You are not an adult";
The ternary operator can be a very useful tool for writing concise and efficient code. It is a good practice to use it whenever possible.
How to use the && operator for conditional statements in JavaScript?
The && operator in JavaScript is a logical AND operator. It is used to combine two or more logical expressions. The && operator returns true if all of the logical expressions evaluate to true. If any of the logical expressions evaluate to false, the && operator returns false.
For example, the following code uses the && operator to check if the value of the variable num is greater than 10 and if the value of the variable num is less than 20:
const num = 15;
const result = num > 10 && num < 20;
console.log(result); // true
The && operator evaluates the first logical expression, which is num > 10. If the first logical expression evaluates to true, the && operator then evaluates the second logical expression, which is num < 20. If the second logical expression also evaluates to true, the && operator returns true. If either of the logical expressions evaluates to false, the && operator returns false.
The && operator can be used to combine any number of logical expressions. The && operator is a short-circuiting operator, which means that it will only evaluate the second logical expression if the first logical expression evaluates to true. This can be useful for improving the performance of your code.
Here are some other examples of using the && operator:
// Check if a number is between 10 and 20
const num = 15;
const result = num >= 10 && num <= 20;
// Check if a user is logged in and has admin privileges
const isLoggedIn = true;
const isAdmin = false;
const result = isLoggedIn && isAdmin;
The && operator can be a very useful tool for writing concise and efficient code. It is a good practice to use it whenever possible.
Explain the difference between if…else and switch statements in JavaScript?
The if...else and switch statements in JavaScript are both conditional statements that are used to execute code based on a condition. However, there are some key differences between the two statements.
The if...else statement is a more general-purpose conditional statement. It can be used to execute code based on any Boolean expression. The switch statement is a more specialized conditional statement. It is designed to be used when you need to execute code based on the value of a variable or expression.
Here is a table that summarizes the key differences between the if...else and switch statements:
Feature |
|
|
|---|---|---|
Purpose | General-purpose conditional statement | Specialized conditional statement |
Syntax |
|
|
When to use | When you need to execute code based on any Boolean expression | When you need to execute code based on the value of a variable or expression |
Here is an example of an if...else statement:
const num = 10;
if (num > 10) {
console.log("The number is greater than 10");
} else {
console.log("The number is not greater than 10");
}
This code first checks if the value of the variable num is greater than 10. If the value of num is greater than 10, the code inside the if block is executed. If the value of num is not greater than 10, the code inside the else block is executed.
Here is an example of a switch statement:
const color = "red";
switch (color) {
case "red":
console.log("The color is red");
break;
case "green":
console.log("The color is green");
break;
case "blue":
console.log("The color is blue");
break;
default:
console.log("The color is not red, green, or blue");
}
This code first checks the value of the variable color. If the value of color is equal to “red”, the code inside the case "red" block is executed. If the value of color is equal to “green”, the code inside the case "green" block is executed. If the value of color is equal to “blue”, the code inside the case "blue" block is executed. If the value of color is not equal to any of the values in the case statements, the code inside the default block is executed.
How to use the ternary operator in a nested conditional statement in JavaScript?
The ternary operator in JavaScript is a shorthand for an if…else statement. It can be used to nest conditional statements.
The syntax of the ternary operator is:
condition ? value_if_true : value_if_false;
The condition is a Boolean expression that evaluates to either true or false. If the condition evaluates to true, the value of the value_if_true expression is returned. If the condition evaluates to false, the value of the value_if_false expression is returned.
Here is an example of a nested conditional statement using the ternary operator:
const num = 10;
const result = num > 5 ? "greater than 5" : num < 5 ? "less than 5" : "equal to 5";
console.log(result); // "greater than 5"
This code first checks if the value of the variable num is greater than 5. If the value of num is greater than 5, the value of the value_if_true expression, which is “greater than 5”, is returned. If the value of num is not greater than 5, the code then checks if the value of num is less than 5. If the value of num is less than 5, the value of the value_if_false expression, which is “less than 5”, is returned. If the value of num is neither greater than 5 nor less than 5, the value of the value_if_false expression, which is “equal to 5”, is returned.
The ternary operator can be used to nest conditional statements in any way you want. It is a very powerful tool for writing concise and efficient code.
Here are some other examples of using the ternary operator in a nested conditional statement:
// Check if a number is between 10 and 20
const num = 15;
const result = num >= 10 ? num <= 20 ? "between 10 and 20" : "greater than 20" : "less than 10";
// Check if a user is logged in and has admin privileges
const isLoggedIn = true;
const isAdmin = false;
const result = isLoggedIn ? isAdmin ? "logged in and has admin privileges" : "logged in" : "not logged in";
The ternary operator can be a very useful tool for writing concise and efficient code. It is a good practice to use it whenever possible.
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