Which example is a valid variable name in JavaScript?

Which example is a valid variable name in JavaScript?

• A. 1name
• B. _firstName
• C. first-name
• D. name1

Answer: (B)

In JavaScript, an identifier (a variable name) must start with a letter, underscore, or dollar sign, and can contain letters, digits, underscores, or dollar signs after the first character. The example that begins with an underscore fits these rules: it starts with an allowed character and contains only letters and underscores, so it’s a valid variable name. The other examples fail for these reasons: starting with a digit isn’t allowed, so the one that begins with a number can’t be a variable name; using a hyphen is invalid because the hyphen is treated as subtraction, not part of an identifier.

In JavaScript, an identifier (a variable name) must start with a letter, underscore, or dollar sign, and can contain letters, digits, underscores, or dollar signs after the first character. The example that begins with an underscore fits these rules: it starts with an allowed character and contains only letters and underscores, so it’s a valid variable name.

The other examples fail for these reasons: starting with a digit isn’t allowed, so the one that begins with a number can’t be a variable name; using a hyphen is invalid because the hyphen is treated as subtraction, not part of an identifier.