[JavaScript] Uncaught Typeerror:method get Set.prototype.size called on incompatible receiver

The Size property cannot be overridden while the set is being extended by method

Scenario: Define a Singletonset, inherit from Set,size can only be 1, and cannot add and remove

The first is the Extend function var extend = (function () {//check for the existence of a bug for (Var p in {Tostring:null}) {//                If it comes in, that means there is no bug return function Extend (o) {for (var i = 1; i < arguments.length; i++) {                var source = Arguments[i];                    For (Var prop in source) {//var desc = object.getownpropertydescriptor (source, prop);                     Object.defineproperty (o, prop, desc);  O[prop] = Source[prop];        The example in the book,}} return o;            }}//If there is a bug, return function Patched_extend (o) {for (var i = 1; i < arguments.length; i++) {            var source = Arguments[i]; Copy the properties that can be enumerated for (Var prop in source) {//var desc = object.getownpropertydescriptor (source, pro                p);                 Object.defineproperty (o, prop, desc);            O[prop] = Source[prop];         }//Check for special properties and copy   for (var j = 0; J < Protoprops.length; J + +) {prop = Protoprops[j];                    if (Source.hasownproperty (prop)) {//var desc = object.getownpropertydescriptor (source, prop);                    Object.defineproperty (o, prop, desc);                O[prop] = Source[prop];    }}} return o; } var protoprops = ["ToString", "ValueOf", "constructor", "hasOwnProperty", "isprototypeof", "Propertyisenumerab Le "," tolocalstring "];}   ());//Call Function Singletonset (member) {this.member = member; This.size = 2;} Singletonset.prototype = Inherit (set.prototype); extend (Singletonset.prototype, {constructor:singletonset, Add:fun        Ction () {throw "Read-only set"}, Remove:function () {throw "Read-only set"}, get Size () {    return 1;    }, Foreach:function (F,context) {f.call (context,this.member); }, Contains:function (x) {return x===this.member; }}); var newset = new Singletonset (1); Console.log (newset.size); Print

Print out to find Newset's Size property error as follows:

After that, you print the test in the Extend function at that location:

  for (var prop in source) {                // var desc = Object.getOwnPropertyDescriptor(source, prop);                // Object.defineProperty(o, prop, desc);                 o[prop] = source[prop];                 console.log(prop);                 console.log(o[prop]);            }

Print as follows:

That is, when executing o[prop] = source[prop]; , the prop===‘size‘ custom method is not assigned to the target object when the error is thrown.

So, my solution, which is commented out, is to make a copy of the Object.defineProperty method to avoid using it o[‘size‘] and throw an error.
The modified extend function is as follows

var extend = (function () {//check for the existence of a bug for (Var p in {Tostring:null}) {//If you come in, that means no bu G return function Extend (o) {for (var i = 1; i < arguments.length; i++) {var source                = Arguments[i];                     For (Var prop in source) {var desc = object.getownpropertydescriptor (source, prop);                    Object.defineproperty (o, prop, desc);  O[prop] = Source[prop];        The example in the book,}} return o;            }}//If there is a bug, return function Patched_extend (o) {for (var i = 1; i < arguments.length; i++) {            var source = Arguments[i];                  Copy the attributes that can be enumerated for (Var prop in source) {var desc = object.getownpropertydescriptor (source, prop);                 Object.defineproperty (o, prop, desc);            O[prop] = Source[prop]; }//Check special properties and copy for (var j = 0; J < Protoprops.length;                J + +) {prop = Protoprops[j];                    if (Source.hasownproperty (prop)) {var desc = object.getownpropertydescriptor (source, prop);                    Object.defineproperty (o, prop, desc);                O[prop] = Source[prop];    }}} return o; } var protoprops = ["ToString", "ValueOf", "constructor", "hasOwnProperty", "isprototypeof", "Propertyisenumerab Le "," tolocalstring "];} ());

At this time

var newSet = new SingletonSet(1);console.log(newSet.size); //打印//结果 为 1,符合预期

[JavaScript] Uncaught Typeerror:method get Set.prototype.size called on incompatible receiver