JavaScript Comparison and Logical Operators

In JavaScript, comparison and logical operators are used to compare values and create logical expressions. Comparison operators are used to compare two values and return a boolean value (true or false). Logical operators are used to combine or invert boolean values.

Comparison Operators

Here are the comparison operators in JavaScript:

• == equal to
• != not equal to
• === strict equal to
• !== strict not equal to
• > greater than
• >= greater than or equal to
• < less than
• <= less than or equal to

The == operator compares two values for equality, while ignoring their data types. The === operator compares two values for strict equality, which means they must have the same value and data type. The != and !== operators are used to test for inequality.

let x = 10;
let y = "10";
console.log(x == y); // true
console.log(x === y); // false
console.log(x != y); // false
console.log(x !== y); // true

Logical Operators

Here are the logical operators in JavaScript:

• && logical AND
• || logical OR
• ! logical NOT

The && operator returns true if both operands are true, otherwise it returns false. The || operator returns true if at least one operand is true, otherwise it returns false. The ! operator inverts the boolean value of its operand.

let x = 10;
let y = 5;
let z = 0;
console.log(x > y && y > z); // true
console.log(x < y || y < z); // false
console.log(!(x > y)); // false

Short-Circuit Evaluation

One interesting feature of logical operators in JavaScript is short-circuit evaluation. This means that the second operand of a logical AND (&&) or logical OR (||) expression is only evaluated if necessary.

let x = 10;
let y = null;
console.log(x && y); // null
console.log(x || y); // 10

In the first example, y is null, which is a falsy value. Therefore, the logical AND expression returns y without evaluating x. In the second example, x is a truthy value, so the logical OR expression returns x without evaluating y.

FAQs

1. What are comparison operators in JavaScript? Comparison operators are used to compare two values and return a boolean value (true or false). Examples of comparison operators in JavaScript include ==, !=, ===, and !==.
2. What are logical operators in JavaScript? Logical operators are used to combine or invert boolean values. Examples of logical operators in JavaScript include &&, ||, and !.
3. What is short-circuit evaluation in JavaScript? Short-circuit evaluation is a feature of logical operators in JavaScript that evaluates the second operand of a logical AND (&&) or logical OR (||) expression only if necessary.
4. What is the difference between == and === in JavaScript? The == operator compares two values for equality, while ignoring their data types. The === operator compares two values for strict equality, which means they must have the same value and data type.
5. What is the boolean value of null in JavaScript? The boolean value of null in JavaScript is false.