The JavaScript exception "missing : after property id" occurs when objects are created
using the object initializer syntax.
A colon (:) separates keys and values for the
object's properties. Somehow, this colon is missing or misplaced.
Message
SyntaxError: Invalid shorthand property initializer (V8-based)
SyntaxError: missing : after property id (Firefox)
SyntaxError: Unexpected token '='. Expected a ':' following the property name 'x'. (Safari)
SyntaxError: Unexpected token '+'. Expected an identifier as property name. (Safari)
Error type
What went wrong?
When creating objects with the object initializer syntax,
a colon (:) separates keys and values for the object's properties.
const obj = { propertyKey: "value" };
Examples
Colons vs. equal signs
This code fails, as the equal sign can't be used this way in this object initializer syntax.
const obj = { propertyKey = "value" };
// SyntaxError: missing : after property id
Correct would be to use a colon, or to use square brackets to assign a new property after the object has been created already.
const obj = { propertyKey: "value" };
Or alternatively:
const obj = {};
obj.propertyKey = "value";
Computed properties
If you create a property key from an expression, you need to use square brackets. Otherwise the property name can't be computed:
const obj = { "b"+"ar": "foo" };
// SyntaxError: missing : after property id
Put the expression in square brackets []:
const obj = { ["b" + "ar"]: "foo" };