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 = true).

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;

See also

• const
• let
• var