Javascript list objects methods

How to list all methods of an object in JavaScript | Javascript get methods of Object

Objects in JavaScript are combinations of key/value pairs. The values can be made up of properties and methods and may include all other JavaScript data types, like strings, numbers, and Booleans. All javascript objects descend from the parent Object constructor .

An Object has many helpful built-in methods we can utilize and access to start working with individual objects straightforward. In this tutorial, you will learn How to list all methods of an object in JavaScript with examples from the below direct links.

JavaScript Object Methods – Example

JavaScript Methods

JavaScript Methods are operations that can be implemented on objects. The definition of a JavaScript method is a property containing a function.

Property	Value
firstName	John
lastName	Doe
age	50
eyeColor	blue
fullName	function()

Accessing Object Methods of JavaScript

Here is the syntax to access the object method:

List all Methods of an Object in JavaScript

We can use the Object.getOwnPropertyNames() function to get all the property names linked to an object.

Then we can filter the resulting array, to only include that property name if it’s a function.

We determine if it’s a function by using typeof on it.

For example here is how we might create a utility function to do what we need:

getMethods = (obj) => Object.getOwnPropertyNames(obj).filter(item => typeof obj[item] === 'function')

This lists only the methods defined on that specific object, not any method defined in its prototype chain.

To do that we must take a slightly different route. We must first iterate the prototype chain and list all the properties in an array. Then we check if each single property is a function.

An easy way to make sure we don’t duplicate methods as we navigate the prototype chain (like constructor which is always present), we use a Set data structure that makes sure values are unique:

const getMethods = (obj) => < let properties = new Set() let currentObj = obj do < Object.getOwnPropertyNames(currentObj).map(item =>properties.add(item)) > while ((currentObj = Object.getPrototypeOf(currentObj))) return [. properties.keys()].filter(item => typeof obj[item] === 'function') >

getMethods("") getMethods(new String('test')) getMethods(<>) getMethods(Date.prototype)

Example on Get all methods of any object JavaScript

const returnMethods = (obj = <>) => < const members = Object.getOwnPropertyNames(obj); const methods = members.filter(el =>< return typeof obj[el] === 'function'; >) return methods; >; console.log(returnMethods(Array.prototype));

Here is the output in the console:

[ 'constructor', 'concat', 'copyWithin', 'fill', 'find', 'findIndex', 'lastIndexOf', 'pop', 'push', 'reverse', 'shift', 'unshift', 'slice', 'sort', 'splice', 'includes', 'indexOf', 'join', 'keys', 'entries', 'values', 'forEach', 'filter', 'flat', 'flatMap', 'map', 'every', 'some', 'reduce', 'reduceRight', 'toLocaleString', 'toString' ]

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JavaScript Array of Objects Tutorial – How to Create, Update, and Loop Through Objects Using JS Array Methods

Ondrej Polesny

On average I work with JSON data 18 times a week. And I still need to google for specific ways to manipulate them almost every time. What if there was an ultimate guide that could always give you the answer?

In this article, I’ll show you the basics of working with object arrays in JavaScript.

If you ever worked with a JSON structure, you’ve worked with JavaScript objects. Quite literally. JSON stands for JavaScript Object Notation.

Creating an object is as simple as this:

This object represents a car. There can be many types and colors of cars, each object then represents a specific car.

Now, most of the time you get data like this from an external service. But sometimes you need to create objects and their arrays manually. Like I did when I was creating this e-shop:

Considering each category list item looks like this in HTML:

I didn’t want to have this code repeated 12 times, which would make it unmaintainable.

Creating an array of objects

But let’s get back to cars. Let’s take a look at this set of cars:

We can represent it as an array this way:

Arrays of objects don’t stay the same all the time. We almost always need to manipulate them. So let’s take a look at how we can add objects to an already existing array.

Add a new object at the start — Array.unshift

To add an object at the first position, use Array.unshift .

Add a new object at the end — Array.push

To add an object at the last position, use Array.push .

Add a new object in the middle — Array.splice

To add an object in the middle, use Array.splice . This function is very handy as it can also remove items. Watch out for its parameters:

So if we want to add the red Volkswagen Cabrio on the fifth position, we’d use:

let car = < "color": "red", "type": "cabrio", "registration": new Date('2016-05-02'), "capacity": 2 >cars.splice(4, 0, car); 

Looping through an array of objects

Let me ask you a question here: Why do you want to loop through an array of objects? The reason I’m asking is that the looping is almost never the primary cause of what we want to achieve.

JavaScript provides many functions that can solve your problem without actually implementing the logic in a general cycle. Let’s take a look.

Find an object in an array by its values — Array.find

Let’s say we want to find a car that is red. We can use the function Array.find .

let car = cars.find(car => car.color === "red"); 

This function returns the first matching element:

It’s also possible to search for multiple values:

let car = cars.find(car => car.color === «red» && car.type === «cabrio»);

In that case we’ll get the last car in the list.

Get multiple items from an array that match a condition — Array.filter

The Array.find function returns only one object. If we want to get all red cars, we need to use Array.filter .

let redCars = cars.filter(car => car.color === "red"); console.log(redCars); // output: // [ // < // color: 'red', // type: 'station wagon', // registration: 'Sat Mar 03 2018 01:00:00 GMT+0100 (GMT+01:00)', // capacity: 5 // >, // < // color: 'red', // type: 'cabrio', // registration: 'Sat Mar 03 2012 01:00:00 GMT+0100 (GMT+01:00)', // capacity: 2 // >// ] 

Transform objects of an array — Array.map

This is something we need very often. Transform an array of objects into an array of different objects. That’s a job for Array.map . Let’s say we want to classify our cars into three groups based on their size.

let sizes = cars.map(car => < if (car.capacity if (car.capacity return "large"; >); console.log(sizes); // output: // ['large','medium','medium', . 'small'] 

It’s also possible to create a new object if we need more values:

let carsProperties = cars.map(car => < let properties = < "capacity": car.capacity, "size": "large" >; if (car.capacity if (car.capacity return properties; >); console.log(carsProperties); // output: // [ // < capacity: 7, size: 'large' >, // < capacity: 5, size: 'medium' >, // < capacity: 5, size: 'medium' >, // < capacity: 2, size: 'small' >, // . // ] 

Add a property to every object of an array — Array.forEach

But what if we want the car size too? In that case we can enhance the object for a new property size . This is a good use-case for the Array.forEach function.

cars.forEach(car => < car['size'] = "large"; if (car.capacity if (car.capacity >); 

Sort an array by a property — Array.sort

When we’re done with transforming the objects, we usually need to sort them one way or another.

Typically, the sorting is based on a value of a property every object has. We can use the Array.sort function, but we need to provide a function that defines the sorting mechanism.

Let’s say we want to sort the cars based on their capacity in descending order.

let sortedCars = cars.sort((c1, c2) => (c1.capacity < c2.capacity) ? 1 : (c1.capacity >c2.capacity) ? -1 : 0); console.log(sortedCars); // output: // [ // < // color: 'purple', // type: 'minivan', // registration: 'Wed Feb 01 2017 00:00:00 GMT+0100 (GMT+01:00)', // capacity: 7 // >, // < // color: 'red', // type: 'station wagon', // registration: 'Sat Mar 03 2018 01:00:00 GMT+0100 (GMT+01:00)', // capacity: 5 // >, // . // ] 

The Array.sort compares two objects and puts the first object in the second place if the result of the sorting function is positive. So you can look at the sorting function as if it was a question: Should the first object be placed in second place?

Make sure to always add the case for zero when the compared value of both objects is the same to avoid unnecessary swaps.

Checking if objects in array fulfill a condition — Array.every, Array.includes

Array.every and Array.some come handy when we just need to check each object for a specific condition.

Do we have a red cabrio in the list of cars? Are all cars capable of transporting at least 4 people? Or more web-centric: Is there a specific product in the shopping cart?

cars.some(car => car.color === "red" && car.type === "cabrio"); // output: true cars.every(car => car.capacity >= 4); // output: false 

You may remember the function Array.includes which is similar to Array.some , but works only for primitive types.

Summary

In this article, we went through the basic functions that help you create, manipulate, transform, and loop through arrays of objects. They should cover most cases you will stumble upon.

If you have a use-case that requires more advanced functionality, take a look at this detailed guide to arrays or visit the W3 schools reference.

Or get in touch with me and I will prepare another article 🙂

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How to List the Properties of a JavaScript Object

In this tutorial, two mostly used methods are presented, which will list the properties of a JavaScript object.

You can use the built-in Object.keys method which is supported in the modern browsers:

let keys = Object.keys(myObj);

Example:

Javascript Object.keys method

To retrieve the list of the property names, you can do the following:

let getKeys = function (obj) < let keysArr = []; for (var key in obj) < keysArr.push(key); >return keysArr; >

Example:

Javascript object list of the property names

Alternatively, you can replace var getKeys with Object.prototype.keys to allow you to call .keys() on any object. However, extending the prototype has some side effects and is not recommended.

You can also use the for. in construct to iterate over an object for its attribute names. However, doing it, you will iterate over all attribute names in the object’s prototype chain. To iterate only over the attributes of the object, you can use the hasOwnProperty() method like this:

for (var key in obj) < if (obj.hasOwnProperty(key)) < /* code here */ > >

Example:

Javascript object hasOwnProperty() method

The Object.keys() method

The Object.keys() method returns the array of a specified object’s own enumerable property names. The property order is the same as in the case of looping over the properties of the object manually.

The hasOwnProperty() Method

The hasOwnProperty() method returns a boolean value that indicates if the object has the specified property as its own property or not. If the object contains the «key» property, a function is created. This would return true if it could find no keys in the loop, meaning the object is empty. If any key is found, the loop breaks returning false.

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