Which example is a valid variable name in JavaScript?

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

Answer: (B)

JavaScript identifiers must start with a letter, a dollar sign, or an underscore, and may continue with letters, digits, dollar signs, or underscores. They cannot start with a digit and they cannot contain hyphens or other punctuation. The underscore-leading example is valid because it begins with an allowed character and uses only permitted characters afterward. The option that starts with a digit breaks the rule and isn’t valid. The one with a hyphen isn’t valid because the hyphen isn’t allowed in identifiers. Digits can appear after the first character, so something like name1 is also valid, but the key point shown here is that starting with an underscore is a perfectly acceptable and common way to name a variable.