Detailed explanation of the properties and instance usage of hasOwnProperty in js

var foo = {
    hasOwnProperty: function() {
        return false;
    },
    bar: 'Here be dragons'
};
foo.hasOwnProperty('bar'); // always returns false
// Use hasOwnProperty of other object and set its context to foo
({}).hasOwnProperty.call(foo, 'bar'); // true

var o = new Object();
o.prop = 'exists';

function changeO() {
 o.newprop = o.prop;
 delete o.prop;
}

o.hasOwnProperty('prop'); // true
changeO();
o.hasOwnProperty('prop'); // false

function foo() {
 this.name = 'foo'
 this.sayHi = function () {
  console.log('Say Hi')
 }
}

foo.prototype.sayGoodBy = function () {
 console.log('Say Good By')
}

let myPro = new foo()

console.log(myPro.name) // foo
console.log(myPro.hasOwnProperty('name')) // true
console.log(myPro.hasOwnProperty('toString')) // false
console.log(myPro.hasOwnProperty('hasOwnProperty')) // fail
console.log(myPro.hasOwnProperty('sayHi')) // true
console.log(myPro.hasOwnProperty('sayGoodBy')) // false
console.log('sayGoodBy' in myPro) // true

var buz = {
  fog: 'stack'
};

for (var name in buz) {
  if (buz.hasOwnProperty(name)) {
    alert("this is fog (" + name + ") for sure. Value: " + buz[name]);
  }
  else {
    alert(name); // toString or something else
  }
}

var foo = {
  hasOwnProperty: function() {
    return false;
  },
  bar: 'Here be dragons'
};

foo.hasOwnProperty('bar'); // always returns false

// If you are concerned about this, you can directly use the real hasOwnProperty method on the prototype chain // Use another object's `hasOwnProperty` and call
({}).hasOwnProperty.call(foo, 'bar'); // true

// You can also use the hasOwnProperty property on the Object prototype Object.prototype.hasOwnProperty.call(foo, 'bar'); // true