Looping through object with hasOwnProperty check?

Question

Is it pointless to use hasOwnProperty in the looping because object will always have properties?

For example:

const fruits = {
    apple: 28,
    orange: 17,
    pear: 54,
}

for (let property in fruits) {
    if (fruits.hasOwnProperty(property)) {
        console.log(fruits[property]);
    } 
}

Answer 1

If you're dealing with a plain object that doesn't inherit from another, such as with the code in your question, yes, the check will be unnecessary. When it'll be useful will be if you're iterating over an object which inherits from another. For example:

const fruit = {
  isEdible: true
}
const apple = Object.create(fruit);
apple.color = 'green';

for (var property in apple) {
    if (apple.hasOwnProperty(property)) {
        console.log(apple[property]);
    } 
}

In this case the hasOwnProperty check is needed to ensure the for..in loop only console.logs properties directly on the apple object - otherwise, properties on the object apple inherits from (that is, fruit) will be printed as well:

const fruit = {
  isEdible: true
}
const apple = Object.create(fruit);
apple.color = 'green';

for (var property in apple) {
  console.log(apple[property]);
}

In the vast majority of cases, it's best to simply use Object.keys (or Object.entries or Object.values) instead, which will iterate over properties directly on the object (ignoring inherited properties):

const fruit = {
  isEdible: true
}
const apple = Object.create(fruit);
apple.color = 'green';

Object.values(apple).forEach((value) => {
  console.log(value);
});

For your code, which is using a plain object literal that doesn't inherit from another (except for from Object, which doesn't have any enumerable properties), it doesn't make a difference - but the functional Object methods are still generally nicer to work with than for..in loops (which are forbidden by many linters)