Javascript setter returns value without validation

Question

JavaScript setter updates the internal value at the reference but the return value is not correct.

var Game = 
{   
    get points() {
        return this._points;
},

    set points(x){        
       x = Math.min(x,25);

       this._points = x;   
       return this._points;
    }
};

Game.points = 10 ;

console.log(Game.points); // outputs 10

var updatedPoints = (Game.points = 60);

console.log(updatedPoints); // outputs 60
console.log(Game.points); // outputs 25

Expected value for 'updatedPoints' was 25 !

Any idea why this could be happening ? Can you suggest if there is a way to fix this ?

Reason to fix this: To make sure the JS code performs as expected , maintainibility !

Answer 1

The JavaScript simple assignement (=) returns the right value as per the specification (11.13.1). This behavior ignores whatever validation happens in your setter.

From the spec:

The production AssignmentExpression : LeftHandSideExpression = AssignmentExpression is evaluated as follows:

1. Let lref be the result of evaluating LeftHandSideExpression.
2. Let rref be the result of evaluating AssignmentExpression.
3. Let rval be GetValue(rref).
4. Throw a SyntaxError exception if the following conditions are all true:
   • Type(lref) is Reference is true
   • IsStrictReference(lref) is true
   • Type(GetBase(lref)) is Environment Record
   • GetReferencedName(lref) is either "eval" or "arguments"
5. Call PutValue(lref, rval).
6. Return rval.

So there is no way to "fix" your issue as it is by design. Checking Game.points should be enough.