js-square-indent-offset

js-square-indent-offset is a variable defined in `js.el'.
Its value is

0

• This variable is safe as a file local variable if its value
  satisfies the predicate `integerp'.

Documentation:
Number of additional spaces for indenting expressions in square braces.
The value must be no less than minus `js-indent-level'.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 24.1 of Emacs.