Question 13

Question

Explain the difference between null, undefined, and NaN.

Answer

1. null:

• Meaning: Represents the intentional absence of a value. It signifies that a variable or property is explicitly set to nothing.

• Example:

  let myVariable = null;  //  We intentionally assigned 'nothing' to myVariable

2. undefined:

• Meaning: Indicates that a variable has been declared but hasn't been assigned a value yet. It's the default state of a variable until you give it a specific value.

• Example:

  let anotherVariable; //  anotherVariable is now 'undefined' because we declared it but didn't assign a value 
  console.log(anotherVariable); // Output: undefined

3. NaN (Not a Number):

• Meaning: Represents an invalid or unrepresentable numerical value. This usually occurs when you perform mathematical operations that result in a non-numeric outcome.

• Example:

  console.log(Math.sqrt(-1)); // Output: NaN 

Key Differences:

• Intent: null is explicit (intentional absence), while undefined is implicit (no value assigned). NaN indicates a computation error.

• Comparison: You cannot directly compare null, undefined, and NaN using == or ===. Use specific checks:

  if (value === null) { /* Handle null */ }
  else if (typeof value === 'undefined') { /* Handle undefined */ }
  else if (isNaN(value)) { /* Handle NaN */ }