This is an experimental technology
Check the Browser compatibility table carefully before using this in production.
The optional chaining operator ?.
permits reading the value of a property located deep within a chain of connected objects without having to expressly validate that each reference in the chain is valid. The ?.
operator functions similarly to the .
chaining operator, except that instead of causing an error if a reference is nullish (null
or undefined
), the expression short-circuits with a return value of undefined
. When used with function calls, it returns undefined
if the given function does not exist.
This results in shorter and simpler expressions when accessing chained properties when the possibility exists that a reference may be missing. It can also be helpful while exploring the content of an object when there's no known guarantee as to which properties are required.
The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.
Syntax
obj?.prop obj?.[expr] func?.(args)
Description
The optional chaining operator provides a way to simplify accessing values through connected objects when it's possible that a reference or function may be undefined
or null
.
For example, consider an object obj
which has a nested structure. Without optional chaining, looking up a deeply-nested subproperty requires validating the references in between, such as:
let nestedProp = obj.first && obj.first.second;
The value of obj.first
is confirmed to be non-null
(and non-undefined
) before then accessing the value of obj.first.second
. This prevents the error that would occur if you simply accessed obj.first.second
directly without testing obj.first
.
With the optional chaining operator (?.
), however, you don't have to explicitly test and short-circuit based on the state of obj.first
before trying to access obj.first.second
:
let nestedProp = obj.first?.second;
By using the ?.
operator instead of just .
, JavaScript knows to implicitly check to be sure obj.first
is not null
or undefined
before attempting to access obj.first.second
. If obj.first
is null
or undefined
, the expression automatically short-circuits, returning undefined
.
This is equivalent to the following:
let nestedProp = ((obj.first === null || obj.first === undefined) ? undefined : obj.first.second);
Optional chaining with function calls
You can use optional chaining when attempting to call a method which may not exist. This can be helpful, for example, when using an API in which a method might be unavailable, either due to the age of the implementation or because of a feature which isn't available on the user's device.
Using optional chaining with function calls causes the expression to automatically return undefined
instead of throwing an exception if the method isn't found:
let result = someInterface.customMethod?.();
Note: If there is a property with such a name and which is not a function, using ?.
will still raise a TypeError
exception (x.y
is not a function
).
Dealing with optional callbacks or event handlers
If you use callbacks or fetch methods from an object with a destructuring assignment, you may have non-existent values that you cannot call as functions unless you have tested their existence. Using ?.
, you can avoid this extra test:
// Written as of ES2019 function doSomething(onContent, onError) { try { // ... do something with the data } catch (err) { if (onError) { // Testing if onError really exists onError(err.message); } } }
// Using optional chaining with function calls function doSomething(onContent, onError) { try { // ... do something with the data } catch (err) { onError?.(err.message); // no exception if onError is undefined } }
Optional chaining with expressions
You can also use the optional chaining operator when accessing properties with an expression using the bracket notation of the property accessor:
let nestedProp = obj?.['prop' + 'Name'];
Examples
Basic example
This example looks for the value of the name
property for the member bar
in a map when there is no such member. The result is therefore undefined
.
let myMap = new Map(); myMap.set("foo", {name: "baz", desc: "inga"}); let nameBar = myMap.get("bar")?.name;
Short-circuiting evaluation
When using optional chaining with expressions, if the left operand is null
or undefined
, the expression will not be evaluated. For instance:
let potentiallyNullObj = null; let x = 0; let prop = potentiallyNullObj?.[x++]; console.log(x); // 0 as x was not incremented
Stacking the optional chaining operator
With nested structures, it is possible to use optional chaining multiple times:
let customer = { name: "Carl", details: { age: 82, location: "Paradise Falls" // detailed address is unknown } }; let customerCity = customer.details?.address?.city; // … this also works with optional chaining function call let duration = vacations.trip?.getTime?.();
Combining with the nullish coalescing operator
The nullish coalescing operator may be used after optional chaining in order to build a default value when none was found:
let customer = { name: "Carl", details: { age: 82 } }; let customerCity = customer?.city ?? "Unknown city"; console.log(customerCity); // Unknown city
Specifications
Specification | Status | Comment |
---|---|---|
Proposal for the "optional chaining" operator | Stage 3 |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Optional chaining operator (?. ) | Chrome
Full support
79
| Edge No support No | Firefox No support No | IE No support No | Opera
Full support
65
| Safari No support No | WebView Android No support No | Chrome Android
Full support
79
| Firefox Android No support No | Opera Android No support No | Safari iOS No support No | Samsung Internet Android No support No | nodejs No support No |
Legend
- Full support
- Full support
- No support
- No support
- Experimental. Expect behavior to change in the future.
- Experimental. Expect behavior to change in the future.
- User must explicitly enable this feature.
- User must explicitly enable this feature.
Implementation Progress
The following table provides a daily implementation status for this feature, because this feature has not yet reached cross-browser stability. The data is generated by running the relevant feature tests in Test262, the standard test suite of JavaScript, in the nightly build, or latest release of each browser's JavaScript engine.