Object.prototype.hasOwnProperty()

const object1 = {};
object1.property1 = 42;

console.log(object1.hasOwnProperty("property1"));
// Expected output: true

console.log(object1.hasOwnProperty("toString"));
// Expected output: false

console.log(object1.hasOwnProperty("hasOwnProperty"));
// Expected output: false

hasOwnProperty(prop)

const fruits = ["Apple", "Banana", "Watermelon", "Orange"];
fruits.hasOwnProperty(3); // true ('Orange')
fruits.hasOwnProperty(4); // false - not defined

const example = {};
example.hasOwnProperty("prop"); // false

example.prop = "exists";
example.hasOwnProperty("prop"); // true - 'prop'   .

example.prop = null;
example.hasOwnProperty("prop"); // true -   null  .

example.prop = undefined;
example.hasOwnProperty("prop"); // true -   undefined  .

const example = {};
example.prop = "exists";

// `hasOwnProperty`   true .
example.hasOwnProperty("prop"); // true
example.hasOwnProperty("toString"); // false
example.hasOwnProperty("hasOwnProperty"); // false

// `in`       true .
"prop" in example; // true
"toString" in example; // true
"hasOwnProperty" in example; // true

const buz = {
  fog: "stack",
};

for (const name in buz) {
  if (buz.hasOwnProperty(name)) {
    console.log(`this is fog (${name}) for sure. Value: ${buz[name]}`);
  } else {
    console.log(name); // toString   
  }
}

const foo = {
  hasOwnProperty() {
    return false;
  },
  bar: "Here be dragons",
};

foo.hasOwnProperty("bar"); //    false .

const foo = { bar: "Here be dragons" };

// Object.hasOwn()  . - 
Object.hasOwn(foo, "bar"); // true

// Object  hasOwnProperty  
Object.prototype.hasOwnProperty.call(foo, "bar"); // true

//  Object hasOwnProperty 
// 'this' call  foo .
({}).hasOwnProperty.call(foo, "bar"); // true

const foo = Object.create(null);
foo.prop = "exists";
foo.hasOwnProperty("prop"); // Uncaught TypeError: foo.hasOwnProperty is not a function