【JavaScript】 プロパティ操作に関するObjectオブジェクトのメソッド

Object.defineProperties(obj, {
    prop2:{
        value:100,
        writable:true,
    },
    prop3:{
        get:function (){ return this.data; },
        set:function (data){ this.data = data; },
    },
});

const arry = [
    ["prop1",100],
    ["prop2",function(){console.log(this.prop1);}]
];
const obj = Object.fromEntries( arry );
  // obj {
  //    prop1 : 100 ,
  //    prop2 : function(){console.log(this.prop1);}
  //  }

obj.prop2(); // 100

const obj = {
    prop1 : 100,
    prop2 : function(){console.log(this.prop1);}
};

const pd = Object.getOwnPropertyDescriptor( obj , "prop1" );

console.log( pd );
  // { value: 100, writable: true, enumerable: true, configurable: true }

const obj = {
    prop1 : 100,
    prop2 : function(){console.log(this.prop1);}
};

  // オブジェクトは、プロトタイプチェーン上にtoStringという名前のメソッドを持っている
console.log( obj.toString() ); // [object Object]

const pd = Object.getOwnPropertyDescriptor( obj , "toString" );

console.log( pd ); // undefine → 取得できなかった

const obj = {
    prop1 : 100,
    prop2 : function(){console.log(this.prop1);},
};

const pd = Object.getOwnPropertyDescriptors( obj  );

console.log( pd );
  // { 
  //    prop1: {value: 100, writable: true, enumerable: true,configurable: true},
  //    prop2: {…},
  // }

const sym = Symbol();

const obj = {
    prop1 : 100,
    prop2 : function(){console.log(this.prop1);},
    [sym] : 300,
};

const oe = Object.entries( obj  );

console.log( oe );  // シンボルは含まれていない
  // [
  //    [ "prop1", 100 ],
  //    [ "prop2", function(){console.log(this.prop1);} ]
  // ]

const sym = Symbol();

const obj = {
    prop1 : 100,
    prop2 : function(){console.log(this.prop1);},
    [sym] : 300,
};
Object.defineProperty( obj , "prop3" , { value:500,enumerable:false} );

const oe = Object.getOwnPropertyNames( obj  );

console.log( oe ); // [ "prop1", "prop2", "prop3" ]

const sym = Symbol();
const sym2 = Symbol();
const obj = {
    prop1 : 100,
    prop2 : function(){console.log(this.prop1);},
    [sym] : 300,
};
Object.defineProperty( obj , sym2 , { value:500,enumerable:false} );

const oe = Object.getOwnPropertySymbols( obj  );

oe.forEach( e => console.log( `${ e.toString() } : ${ obj[e] }` ) );
  // Symbol() : 300
  // Symbol() : 500

const sym = Symbol();

const obj = {
    prop1 : 100,
    prop2 : function(){console.log(this.prop1);},
    [sym] : 300,
};
Object.defineProperty( obj , "prop3" , { value:500,enumerable:false} );

const oe = Object.keys( obj  );
console.log( oe ); // [ "prop1", "prop2" ]

const sym = Symbol();

const obj = {
    prop1 : 100,
    prop2 : function(){console.log(this.prop1);},
    [sym] : 300,
};
Object.defineProperty( obj , "prop3" , { value:500,enumerable:false} );

const oe = Object.values( obj  );
console.log( oe ); // [ 100, function(){console.log(this.prop1);} ]

const obj = {
    prop1 : 100,
};
const op = Object.getPrototypeOf(obj);
console.log( Object.is( op , Object.prototype ));

const obj = {
    prop1 : 100,
};
const obj2 = {
    method : function (){ console.log( this.prop1 );},
};
Object.setPrototypeOf(obj, obj2);

obj.method(); // 100