The JavaScript exception "missing = in const declaration" occurs when a const
declaration was not given a value in the same statement (like
const RED_FLAG;). You need to provide one
(const RED_FLAG = "#ff0").
Message
SyntaxError: Missing initializer in const declaration (V8-based)
SyntaxError: missing = in const declaration (Firefox)
SyntaxError: Unexpected token ';'. const declared variable 'x' must have an initializer. (Safari)
Error type
What went wrong?
A constant is a value that cannot be altered by the program during normal execution. It
cannot change through re-assignment, and it can't be redeclared. In JavaScript,
constants are declared using the
const
keyword. An initializer for a constant is required; that is, you must specify its value
in the same statement in which it's declared (which makes sense, given that it can't be
changed later).
Examples
Missing const initializer
Unlike var or let, you must specify a value for a
const declaration. This throws:
const COLUMNS;
// SyntaxError: missing = in const declaration
Fixing the error
There are multiple options to fix this error. Check what was intended to be achieved with the constant in question.
Adding a constant value
Specify the constant value in the same statement in which it's declared:
const COLUMNS = 80;
const, let or var?
Do not use const if you weren't meaning to declare a constant. Maybe you
meant to declare a block-scoped variable with
let or
global variable with
var. Both
don't require an initial value.
let columns;