Given the following JavaScript code: ```javascript var n1 = 10; var n2 = "20.39"; ``` Which function should a developer use to convert the content of…

Question breakdown

Tests

Convert strings to numbers in JavaScript

Difficulty

Easy

Key idea: parseFloat() parses a string and returns a floating-point number, keeping the fractional part.

How to reach the answer

1. The variable n2 holds the string "20.39".
2. The requirement is to keep the decimal places, so an integer-only conversion is ruled out.
3. parseInt would return 20 and drop .39.
4. parseFloat("20.39") returns 20.39, which meets the requirement.

Each option

• AIncorrect. isNaN only tests whether a value is Not-a-Number and returns a boolean; it converts nothing.
• BIncorrect. parseInt returns an integer, so the decimal portion .39 is lost.
• CCorrect. parseFloat returns a floating-point number, so "20.39" becomes 20.39.
• DIncorrect. toUpperCase is a string method that changes letter case; it returns a string, not a number.

Common trap: parseInt looks like the generic way to turn a string into a number, but it discards everything after the decimal point.

In practice: Values read from form inputs or query strings arrive as strings. Prices, measurements, and similar values need parseFloat (or Number) before you do arithmetic on them.

Remember: Use parseFloat to keep decimals and parseInt when you want a whole number.

Drafted with AI assistance and checked against the answer key.