JavaScript Object freeze

Written by Swapnil RajaPublished 24 Aug 2026

Object.freeze stops an object being changed after it is created.

const only stops the variable being reassigned, not the object being edited.

Object.freeze is what actually locks the contents.

Example

javascript

const settings = Object.freeze({ theme: "dark" });

settings.theme = "light";

console.log(settings.theme);

The assignment is ignored and the value stays dark.

In strict mode it would throw an error instead.

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Example

javascript

function deepFreeze(object) {
  Object.values(object).forEach(function (value) {
    if (value && typeof value === "object") deepFreeze(value);
  });
  return Object.freeze(object);
}

const config = deepFreeze({ db: { host: "local" } });
config.db.host = "remote";

console.log(config.db.host);

Complete Example

html

<!DOCTYPE html>
<html>
<head>
  <title>JavaScript Object.freeze</title>
</head>
<body>

  <h1>JavaScript Object.freeze</h1>

  <p id="result"></p>

  <script>
    const settings = Object.freeze({ theme: "dark", size: "medium" });

    settings.theme = "light";

    document.getElementById("result").innerHTML =
      "theme: " + settings.theme +
      "<br>frozen: " + Object.isFrozen(settings);
  </script>

</body>
</html>

JavaScript Object freeze

Example

freeze and seal

Syntax

const is Not Enough

Example

Checking if Frozen

Example

seal Allows Edits

Example

Freezing is Shallow

Example

Freezing Deeply

Example

Complete Example

Try It Yourself

Important Points

Conclusion