How to use JavaScript parseFloat()? [SOLVED]

parseFloat() is an internal JavaScript function that takes a string and turns it into a floating-point number (a number with decimal places).

Imagine it as a translator:

• You feed it text that resembles a number.
• It returns a actual number JavaScript can perform math on.

 

Basic Usage

let num = parseFloat("3.14");
console.log(num); // 3.14 (as a number, not a string)
console.log(typeof num); // "number"

If you attempt to do math using the original string, it doesn't work:

"3.14" * 2; // 6.28 (works, but JS coerces automatically)
"3.14" + 2; // "3.142" (string concatenation!)

With parseFloat(), you're in control:

parseFloat("3.14") + 2; // 5.14

 

Dealing with Extra Spaces or Characters

parseFloat() is tolerant:

• It ignores leading/trailing white space.
• It reads until it encounters non-numeric strings.

console.log(parseFloat("   42.5 ")); // 42.5
console.log(parseFloat("99 bottles")); // 99
console.log(parseFloat("bottles 99")); // NaN (Not a Number)

 

Special Cases

NaN: If it can't find anything that's a number, you get NaN.

parseFloat("hello"); // NaN

Scientific notation does work:

parseFloat("1.23e4"); // 12300

Integers still do work (just no decimals):

parseFloat("100"); // 100

 

Common Use Cases

User input (from forms)

let price = "49.99";  // comes as string
let tax = 0.05;
let total = parseFloat(price) * (1 + tax);
console.log(total); // 52.4895

Extracting numbers from sloppy strings

parseFloat("$123.45"); // NaN
parseFloat("123.45 USD"); // 123.45

(If currency symbols are first, you might need to tidy the string.)

When precision is important

parseFloat() returns decimals. Use it if you anticipate fractional numbers.
If you only need whole numbers, use parseInt().

 

Advanced Tips

Check if parsing was successful

let val = parseFloat("hello");
if (isNaN(val)) {
  console.log("Not a valid number");
}

Working with arrays of number strings

let arr = ["1.1", "2.2", "3.3"];
let nums = arr.map(parseFloat);
console.log(nums); // [1.1, 2.2, 3.3]

Difference from Number()

Number("123.45abc"); // NaN
parseFloat("123.45abc"); // 123.45

So:

• Use Number() for strict conversion.
• Use parseFloat() if you want to get the leading number out of a string.

 

Quick Gotchas

• parseFloat(" ") → NaN (empty string).
• parseFloat(null) → NaN.
• parseFloat(true) → NaN.
• parseFloat(3.14) → 3.14 (already a number, stays the same).

 

Summary

• Use parseFloat() to safely convert strings to decimal numbers.
• It reads up to the first non-number character, then stops.
• Use isNaN() to determine if the result is valid.
• Opt for Number() if you want to be more stringent.