SyntaxError: setter functions must have one argument
The JavaScript exception "setter functions must have one argument" occurs when a setter is declared and the parameter list is not consisted of exactly one formal parameter.
Message
SyntaxError: Setter must have exactly one formal parameter. (V8-based)
SyntaxError: Setter function argument must not be a rest parameter (V8-based)
SyntaxError: setter functions must have one argument (Firefox)
SyntaxError: Unexpected token ','. setter functions must have one parameter. (Safari)
SyntaxError: Unexpected token '...'. Expected a parameter pattern or a ')' in parameter list. (Safari)
Error type
What went wrong?
The set property syntax looks like a function, but it is stricter and not all function syntax is allowed. A setter is always invoked with exactly one argument, so defining it with any other number of parameters is likely an error. This parameter can be destructured or have a default value, but it cannot be a rest parameter.
Note that this error only applies to property setters using the set syntax. If you define the setter using {{jsxref("Object.defineProperty()")}}, etc., the setter is defined as a normal function, although it's likely still an error if the setter expects any other number of arguments, as it will be called with exactly one.
Examples
Invalid cases
const obj = {
set value() {
this._value = Math.random();
},
};
Valid cases
// You must declare one parameter, even if you don't use it
const obj = {
set value(_ignored) {
this._value = Math.random();
},
};
// You can also declare a normal method instead
const obj = {
setValue() {
this._value = Math.random();
},
};