Javascript setter返回值而不进行验证

JavaScript setter更新引用的内部值,但返回值不正确.

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

‘updatedPoints’的预期价值是25！

知道为什么会发生这种情况吗？你能否建议是否有办法解决这个问题？

解决此问题的原因：确保JS代码按预期执行,可维护性！

解决方法:

JavaScript simple assignement(=)根据规范(11.13.1)返回正确的值.此行为忽略了setter中发生的任何验证.

从规格：

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.

所以没有办法按照设计“修复”你的问题.检查Game.points就足够了.

标签：javascript,javascript-objects,getter-setter,ecmascript-5,javascript-engine
来源： https://codeday.me/bug/20190825/1717286.html