Square Brackets
in JavaScript
This is an entry in Marek's JavaScript Compendium. Last updated 2020-04-08.
in JavaScript
This is an entry in Marek's JavaScript Compendium. Last updated 2020-04-08.
Square brackets are punctuation marks that always come in a pair: the opening square bracket [ and the closing square bracket ].
[ ]
Square brackets have 3 possible meanings.
Square brackets are used in array expressions.
An empty array is created with an empty array expression. Empty arrays are the only situation where a pair of square brackets can be exist without anything in between them.
An array expression
[alpha, bravo, charlie];
An empty array expression
[];
Square brackets are one of the two possible ways to access a property. The square bracket method allows you to provide the property name
Access an array value by its index
alpha[0]
alpha[i]
Access a property
bravo["length"]
bravo[charlie]
When creating an object, you can use square brackets to provide a computed value for a key.
``js const customPropertyName = "alpha";
const gammaObject = { [customPropertyName] = "bravo" }; ``
You can use the square brackets in the left-hand-side of an assignment. This destructures the assignment, assuming that the value on the right-hand-side is an array.
const [first, second] = charlie;
That covers the different situations where square brackets can appear.
Read about the other types of brackets in JavaScript below.