JavaScript parseInt and parseFloat

Written by Swapnil RajaPublished 24 Aug 2026

parseInt and parseFloat read a number from the start of a string.

Unlike Number, they ignore whatever follows the number.

That is sometimes helpful and sometimes a trap.

Example

javascript

console.log(parseInt("42px"));
console.log(Number("42px"));

The output is 42 then NaN.

parseInt stopped at the first character it could not use.

How They Differ from Number

Number requires the whole string to be a number.

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Complete Example

html

<!DOCTYPE html>
<html>
<head>
  <title>JavaScript parseInt</title>
</head>
<body>

  <h1>parseInt and parseFloat</h1>

  <p id="out"></p>

  <script>
    const width = "250px";
    const price = "19.99 pounds";

    document.getElementById("out").innerHTML =
      "Width plus 50: " + (parseInt(width, 10) + 50) +
      "<br>Price: " + parseFloat(price) +
      "<br>Number would give: " + Number(width);
  </script>

</body>
</html>

JavaScript parseInt and parseFloat

Example

How They Differ from Number

Syntax

Whole Numbers Only

Example

Reading CSS Values

Example

The Radix Argument

Example

When Nothing Can Be Read

Example

Which One to Use

Example

Complete Example

Try It Yourself

Important Points

Conclusion