JavaScript String bold() Method

Beginner
5 min read
Updated: Nov 2026
3 examples
Method
Decorative image with the word BOLD

Definition

String.prototype.bold() is a legacy HTML wrapper that returns a new string wrapping your text in <b>…</b>. It takes no parameters and never mutates the original string.

Pass the required arguments shown below. Check return values and browser support before you rely on the result.

Syntax

Call string.bold. Start with this line.

JavaScript
string.bold()
CallWhat it does
string.bold()Primary signature.
string.bold(...)Call with the arguments your case needs.

Built into JavaScript. Call bold(...) on a string (or String instance) — no import required.

Library declarations
JavaScript
string.bold()

Parameters

This member has no parameters beyond those shown in the signature.

Return Value

Return ValueDescription
*HTML string with <b> tags

JavaScript Examples

Example 1 — Basic Wrap

Call bold() to build the classic <b> HTML string.

JavaScript
const text = "Hello, world";

console.log(text.bold());
// "<b>Hello, world</b>"
Try It Yourself

How It Works

  1. Start with text. "Hello, world" is a normal string.
  2. Call bold(). No arguments — the method wraps the whole string.
  3. Get HTML markup. The return value is "<b>Hello, world</b>".
  4. Original stays put. text is still "Hello, world".

Example 2 — Empty String & Special Characters

See empty wrappers and that < is not escaped.

JavaScript
console.log("".bold());       // "<b></b>"
console.log("A < B".bold());  // "<b>A < B</b>"
console.log(typeof "x".bold()); // "string"
Try It Yourself

How It Works

  1. Empty input. "".bold() still wraps tags around nothing → "<b></b>".
  2. No escaping. "A < B" keeps the < character inside the markup.
  3. Type is string. You get text, not a live DOM element.
  4. Safety tip. Never feed untrusted input through bold() into innerHTML.

Example 3 — Prefer DOM / <strong>

Compare the legacy wrapper with a modern, semantic approach.

JavaScript
// Legacy — do not use in new code
console.log("Important".bold());
// "<b>Important</b>"

// Prefer DOM + semantic emphasis
const el = document.createElement("strong");
el.textContent = "Important";
console.log(el.outerHTML);
// "<strong>Important</strong>"
Try It Yourself

How It Works

  1. Legacy path. "Important".bold() builds a <b> HTML string.
  2. Create a real element. createElement("strong") marks strong importance.
  3. Set plain text. textContent is safer than injecting markup strings.
  4. Rule of thumb. Learn bold() to read old code; ship DOM or CSS for new UI.
Compatibility

Browser & Runtime Support

String.prototype.bold() is still implemented widely for compatibility, but it is deprecated. Do not use it in new projects.

✓ Deprecated · Legacy

String.prototype.bold()

Available in major browsers and Node.js for legacy compatibility. Prefer DOM APIs, CSS font-weight, or <strong> for new code.

Legacy Compatibility only
Google Chrome Supported · Desktop & Mobile
Full support
Mozilla Firefox Supported · Desktop & Mobile
Full support
Apple Safari Supported · macOS & iOS
Full support
Microsoft Edge Supported · Chromium
Full support
Internet Explorer No native support · Use a polyfill
Polyfill
Opera Supported · Modern versions
Full support
Samsung Internet Supported · Android
Full support
Bun Supported · JavaScript runtime
Supported
Deno Supported · JavaScript runtime
Supported
Node.js Supported · Server runtime
Supported
Android WebView Supported · Modern WebView
Full support
bold() Avoid in new code

Bottom line: Recognize bold() when reading old code. For new UI, create elements with textContent, use CSS font-weight, or semantic <strong> — never build markup with string wrappers.

Frequently Asked Questions

bold() returns a new HTML string that wraps the text in a <b> element — for example "Hello".bold() returns "<b>Hello</b>". It takes no parameters and does not change the original string.
Yes. MDN marks all HTML wrapper methods as deprecated. Prefer document.createElement(), CSS font-weight, or a semantic <strong> element when the text is important.
Yes. Unlike <blink> or <big>, <b> is still in HTML. Use it to draw attention without extra importance. Use <strong> when the text has strong importance, or CSS font-weight for visual weight alone.
No. Strings are immutable. bold() returns a new string containing markup; the original text stays the same.
Use document.createElement("b") or createElement("strong"), set textContent, and append the element. Or apply CSS font-weight without building HTML strings.
No. Characters like < and > are left as-is inside the wrapper. Never pass untrusted user input through bold() into innerHTML.

Next: fixed()

Another deprecated HTML wrapper — this one builds <tt> (teletype) markup.

fixed() tutorial →

About the author

Mari Selvan M P
Mari Selvan M P 🔗

Developer, cloud engineer, and technical writer

  • Experience 12 years building web and cloud systems
  • Focus Full Stack Development, AWS, and Developer Education

I write practical tutorials so students and working developers can learn by doing—from databases and APIs to deployment on AWS.

AWS Certified Developer – Associate (Credly)

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