JavaScript String(): Convert Numbers to Strings

Use String(value) to convert a number to a JavaScript string. The returned value has the type string; adding two converted values with + joins their text instead of adding the numbers. String() also accepts values such as booleans, null and undefined.

String() syntax and return value

String(value)
String(123)       // "123"
String(0)         // "0"
typeof String(12) // "string"

Pass the value or variable you want to convert. The typeof operator identifies its type: the number 12 and the string "12" can look identical on a page but behave differently in calculations and comparisons. MDN explains the function and constructor forms of String().

Complete example: addition versus concatenation

Save the following code as string-example.html in UTF-8 and open it in a browser. It requires no library. The result is assigned to textContent, which displays text without interpreting it as HTML.

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>String() and numeric addition</title>
  <style>
    body { margin: 24px; font: 16px/1.7 sans-serif; }
    input, button, select { font: inherit; max-width: 100%; }
    label { display: block; margin-top: 12px; }
    #output { white-space: pre-wrap; overflow-wrap: anywhere; }
  </style>
</head>
<body>
<p>Compare numeric addition with string concatenation.</p>
  <pre id="output" aria-live="polite"></pre>
  <script>
    const a = 1;
    const b = 2;
    const values = [123, 0, false, null, undefined];
    const lines = [
      `Numeric addition: ${a + b}`,
      `String concatenation: ${String(a) + String(b)}`,
      `Converted type: ${typeof String(a)}`
    ];
    for (const value of values) {
      lines.push(`${typeof value} value → ${JSON.stringify(String(value))}`);
    }
    document.getElementById("output").textContent = lines.join("\n");
  </script>
</body>
</html>

The first two lines show Numeric addition: 3 and String concatenation: 12. The remaining lines include "123", "0", "false", "null" and "undefined". Here, JSON.stringify() adds quotation marks to make the returned strings easier to recognize; it is not required for the conversion itself.

Handle missing values and objects deliberately

If null or undefined should produce no visible text, choose a fallback before converting. The ?? operator uses its right operand only when the left operand is null or undefined, so it preserves valid values such as 0 and false.

const value = null;
const text = String(value ?? "");
console.log(text); // empty string

String({ count: 3 });            // "[object Object]"
JSON.stringify({ count: 3 });    // '{"count":3}'

JSON, or JavaScript Object Notation, is a text format for structured data. Serializing an object with JSON.stringify() can expose its properties more clearly than String(), which commonly produces "[object Object]" for plain objects. JSON serialization has limitations, including circular references. For digit grouping and decimal display options, use number formatting and thousands separators rather than expecting String() to apply a locale.

String() and new String() are different

const primitive = String(123);
const wrapper = new String(123);

typeof primitive;       // "string"
typeof wrapper;         // "object"
primitive === "123";    // true
wrapper === "123";      // false

Call String() without new for ordinary conversion. new String() creates a wrapper object, so its type is object and it is not strictly equal to a primitive string. Strict equality, written ===, compares values without automatically converting their types. To calculate with text again, use Number() conversion and input validation and check that the input is acceptable before using the result.