parseFloat() is a JavaScript global function that parses a string and returns a floating-point number. It reads the string from the beginning, extracting numeric characters until it encounters a non-numeric character, then stops and returns the parsed number. If the first non-whitespace character cannot form a valid number, it returns NaN (Not a Number).

• Syntax: parseFloat(string)

• Input: A string (or value coerced to a string).

• Output: A floating-point number, or NaN if parsing fails.

• Key behavior: Ignores leading whitespace, stops at the first invalid character, and supports decimal points, scientific notation (e or E), and Infinity/-Infinity when specified.

Examples

parseFloat("3.14");           // Returns 3.14
parseFloat("  42.5  ");       // Returns 42.5 (ignores spaces)
parseFloat("123abc");         // Returns 123 (stops at 'a')
parseFloat("abc123");         // Returns NaN (first char invalid)
parseFloat("1.7976931348623159e+308"); // Returns Infinity

Using with toFixed() for 2 Decimal Places

To format a parsed float to 2 decimal places, combine parseFloat() with toFixed(2):

let num = parseFloat("10.547892");
console.log(num.toFixed(2));  // Returns "10.55" (as a string)

Note: toFixed() returns a string. Use parseFloat() again if you need a number.

parseFloat() vs Number()

• parseFloat() is more lenient: it ignores trailing invalid characters.

• Number() returns NaN if the entire string isn’t a valid number (e.g., Number("123abc") → NaN, while parseFloat("123abc") → 123).

Number.parseFloat() (Alternative)

Number.parseFloat() is equivalent to the global parseFloat() and is preferred in modern code for clarity and consistency.

Note: parseFloat() does not support non-decimal literals like 0x (hex), 0b (binary), or 0o (octal).