References

Beginner-friendly references for web development, with live, editable examples.

The JavaScript Object object

Object JavaScript All modern browsers Updated
Quick answer

The Object is JavaScript's key-value structure — properties mapping names to values. Create one with a literal { name: "Ada" }. Read or loop its data with the static helpers Object.keys(), Object.values() and Object.entries(), and merge objects with Object.assign() or the spread operator.

Overview

The Object is the fundamental key-value structure in JavaScript — a bag of named properties. You create one with a literal: const user = { name: "Ada", age: 36 }. Read properties with dot notation (user.name) or brackets for dynamic keys (user[key]), add new ones by assigning, and remove them with delete. Values can be anything: numbers, strings, arrays, functions, other objects.

Because plain objects don't have map() or forEach(), the Object constructor provides static helpers to bridge to arrays: Object.keys() gives the property names, Object.values() gives the values, and Object.entries() gives [key, value] pairs you can loop with for...of. To merge objects, Object.assign() or the spread syntax {...a, ...b} do the job.

A couple more useful members: Object.freeze() makes an object read-only, and Object.hasOwn(obj, key) checks for an own property. When you need true key-value mapping with non-string keys, ordered iteration or frequent additions and deletions, a Map is sometimes a better fit than a plain object — but for structured records, the object literal is the everyday default.

Syntax

const user = { name: "Ada", age: 36 };

user.name;            // "Ada"
user["age"];          // 36
user.role = "admin";  // add
delete user.age;      // remove

Object.keys(user);    // ["name", "role"]

Example

Live example 
<pre id="out" style="font:15px ui-monospace,monospace"></pre>
<script>
  const book = { title: 'JS Guide', pages: 320, author: 'Ada' };

  const summary = Object.entries(book)
    .map(([key, value]) => key + ': ' + value)
    .join('\n');

  document.getElementById('out').textContent = summary;
</script>

Best practices

  • Create objects with literals {} and access properties with dot notation where possible.
  • Loop with Object.entries() (or keys()/values()) to use array methods on object data.
  • Merge with the spread syntax {...a, ...b} or Object.assign().
  • Consider a Map when you need non-string keys, ordering guarantees or frequent add/remove.

Frequently asked questions

How do I create an object in JavaScript?
Use an object literal: const obj = { key: "value" }. Read properties with obj.key or obj["key"].
How do I loop over an object?
Turn its data into arrays with Object.keys(), Object.values() or Object.entries(), then loop those.
How do I merge two objects?
Use the spread syntax {...a, ...b} or Object.assign({}, a, b). Later properties win.
What is the difference between an object and a Map?
A plain object uses string/symbol keys and suits structured records; a Map allows any key type, preserves insertion order and is better for frequent additions and deletions.
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