JavaScript Logical Operators: OR, AND, NOT
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Questions and Answers

What is the result of the OR operator when both operands are false?

  • null
  • undefined
  • false (correct)
  • true

    • What is the purpose of the OR operator in an if statement?

  • To test if any of the given conditions is true (correct)
  • To assign a value to a variable
  • To check if all conditions are true
  • To throw an error

    • What happens when an operand is not a boolean in JavaScript?

  • It is returned as it is
  • It is converted to a boolean (correct)
  • It is ignored
  • It throws an error

    • What is the result of the OR operator when one of its operands is true?

    <p>It always returns true</p> Signup and view all the answers

    What is the behavior of the OR operator in JavaScript when given multiple OR'ed values?

    <p>It returns the first truthy value</p> Signup and view all the answers

    What is the primary function of the OR || operator in JavaScript?

    <p>To return the first truthy value in a chain of OR operations</p> Signup and view all the answers

    What is the significance of short-circuit evaluation in the OR || operator?

    <p>It stops the evaluation immediately upon seeing a truthy value</p> Signup and view all the answers

    What is the difference between the OR || and AND && operators?

    <p>OR returns the first truthy value, while AND returns the first falsy value</p> Signup and view all the answers

    What is the purpose of the double NOT!! operator in JavaScript?

    <p>To convert a value to a boolean type</p> Signup and view all the answers

    What will be the output of the expression alert("not printed") || true || alert("printed")?

    <p>Neither message will be printed</p> Signup and view all the answers

    Study Notes

    OR Operator Behavior

    • The OR operator (||) returns false when both operands are false.
    • The OR operator evaluates to true when at least one operand is true.
    • In JavaScript, an operand that is not explicitly a boolean is automatically converted to one.
      • This means a falsy value like 0, null, undefined, "", or NaN is treated as false, while truthy values like 1, 'hello', or an object are treated as true.
    • The OR operator evaluates from left to right and stops as soon as it finds a truthy value.
      • This is known as short-circuit evaluation.

    Purpose of OR Operator

    • The OR operator is used in if statements to execute code only if at least one condition is met.

    Short-Circuit Evaluation

    • Short-circuit evaluation is a key feature of the OR operator.
    • It prevents evaluating subsequent operands if the first one is already truthy.
    • This can be used for various purposes, including:
      • Early exit from complex expressions.
      • Avoiding unnecessary computations.

    Comparison with AND Operator

    • Unlike the OR operator, the AND operator (&&) returns true only when both operands are true.
    • The AND operator also uses short-circuit evaluation.
    • It stops evaluating when it encounters a falsy value since the entire expression will be false regardless of the remaining operands.

    Double Negative Operator !!

    • The double negative operator (!!) is used to explicitly convert any value to a boolean.
    • This is helpful for situations where you need to explicitly check if a value is truthy or falsy.

    Example Output

    • The expression alert("not printed") || true || alert("printed") will only execute alert("not printed").
    • This is due to short-circuit evaluation. The OR operator evaluates from left to right, and upon encountering true, it stops further evaluation, skipping the execution of alert("printed").

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    Description

    Learn about the first three logical operators in JavaScript, including the OR, AND, and NOT operators, and how they can be applied to values of any type. Understand how they work and their results.

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