JavaScript object syntax starts with an object initializer, also called an object literal: put properties between braces to create an object. For example, const person = { name: "Ada", age: 36 };. The braces can also hold methods, computed property names, and spread expressions—but object creation, property access, and destructuring are related, distinct operations.
Create an object with an object initializer
An object initializer creates an object and defines its initial properties. Each property has a key and a value; a value can be a string, number, another object, or any JavaScript expression.
const car = {
make: "Ford",
model: "Mustang",
year: 1969,
};The const declaration prevents reassignment of the car binding, but it does not make the object immutable: its properties can still be changed or added.
Choose property names and access them
Object property keys are strings or symbols. Identifier-like names can be written without quotes; names that include spaces or other characters outside identifier syntax are usually quoted. Numeric keys are converted to strings for ordinary property-key use, and names are case-sensitive.
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const record = {
name: "Ada",
"date created": "Monday",
2: "second index-like key",
};
record.name; // dot access
record["date created"]; // bracket access
const key = "name";
record[key]; // computed accessUse dot notation when the property name is a fixed identifier-like name. Use brackets when the name has spaces or when a variable or expression supplies the key at runtime. In an initializer, [key]: value computes a key while creating the object; after creation, object[key] accesses the property selected by key.
Use shorthand and computed property names
If a variable and the property you want have the same name, write the name once. A shorthand property such as { name } means the same as { name: name }. Put an expression in square brackets to calculate a property name.
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const name = "Ada";
const field = "score";
const result = {
name,
[field]: 10,
[`level${2}`]: "two",
};Define methods and accessors
A function stored as a property can be called as a method. Method shorthand lets you write increment() { ... } rather than giving the property a traditional function-expression value. Getters and setters define behavior for reading and assigning a property.
const counter = {
value: 0,
increment() {
this.value += 1;
},
get current() {
return this.value;
},
set current(next) {
this.value = next;
},
};Use spread to copy or merge properties
Object spread copies an object’s enumerable own properties into a new object. When multiple sources or explicit properties use the same key, the later value wins, so the order matters.
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const defaults = { theme: "light", pageSize: 20 };
const preferences = { theme: "dark" };
const settings = { ...defaults, ...preferences, pageSize: 50 };
// { theme: "dark", pageSize: 50 }This is a shallow copy: nested object values remain references to the same nested objects, and spread does not copy the source object’s prototype.
Tell object creation apart from access, spread, and destructuring
These forms are often taught together because they work with object properties, but they do different jobs.
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| Form | Purpose | Example |
|---|---|---|
| Object initializer | Create an object | { name: "Ada" } |
| Dot access | Read a fixed identifier-like property | person.name |
| Bracket access | Read a non-identifier or computed property | person[key] |
| Destructuring | Bind selected property values to variables | const { name } = person |
| Spread | Shallow-copy or merge enumerable own properties | { ...defaults, ...overrides } |
Destructuring extracts values from an existing object; it does not create an object literal:
const user = { name: "Ada", role: "editor" };
const { name, role } = user;Object literals are not JSON
An object literal is executable JavaScript syntax, while JSON is a data interchange format with stricter rules. JavaScript object initializers can contain expressions, shorthand properties, methods, computed keys, and spread. JSON does not allow those features and requires property names to be quoted. An object literal is therefore not automatically valid JSON. See MDN’s object initializer reference for the syntax distinction.
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Where to check the language rules
For more detail, see MDN’s guide to working with objects for object properties and access notation, the object initializer reference for methods, computed properties, and spread, and MDN’s destructuring reference for property extraction.
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