List keys in object javascript

How to Get All Keys (Including Symbols) from an Object in JavaScript or Node.js

We recently added a new feature to the @supercharge/map package: create a map from an object. Objects and maps represent key-value pairs. We iterated through the object’s keys to create the related entries in the map.

While iterating through the object keys, we noticed that properties were missing in the used for…in loop. For example, symbols or non-enumerable properties weren’t available in the map. But they were on the object! Why are they missing?

This tutorial shows you how to retrieve all keys of an object, including symbols!

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Get All Keys Including Symbols From a JavaScript Object

JavaScript objects can have non-enumerable properties. Non-enumerable properties are available when accessing them directly, like obj.nonEnumerableProperty . But these properties won’t show up when looping over an object’s properties using a for…in loop.

You can find more details about an object’s property enumerability in the MDN docs.

A way to iterate through all properties of an object is using the Reflect.ownKeys method. Reflect.ownKeys returns the list of enumerable, non-enumerable, and symbol keys of a given object.

Here’s a sample function returning the keys of a given obj ect:

/** * Returns all keys from the given `obj`ect. * * @returns > */ function keysOf(obj)

You may use the keysOf function like this:

const users = < 1: 'Marcus', 'user:2': 'Norman', [Symbol.for('christian')]: 'Christian' >const keys = keysOf(users) // ['1', 'user:2', Symbol(christian)] 

Please notice: Reflect.ownKeys() doesn’t return inherited enumerable properties. This can happen when working with class inheritance. You may not retrieve the properties of your base class using this approach with an inherited class instance.

Also, notice that JavaScript coerces all keys to a string. The example contains a key-value pair 1: ‘Marcus where the key 1 is a number. Everything is a string when retrieving an object’s keys in JavaScript.

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Object.keys()

The Object.keys() static method returns an array of a given object’s own enumerable string-keyed property names.

Try it

Syntax

Parameters

Return value

An array of strings representing the given object’s own enumerable string-keyed property keys.

Description

Object.keys() returns an array whose elements are strings corresponding to the enumerable string-keyed property names found directly upon object . This is the same as iterating with a for. in loop, except that a for. in loop enumerates properties in the prototype chain as well. The order of the array returned by Object.keys() is the same as that provided by a for. in loop.

If you need the property values, use Object.values() instead. If you need both the property keys and values, use Object.entries() instead.

Examples

Using Object.keys()

// Simple array const arr = ["a", "b", "c"]; console.log(Object.keys(arr)); // ['0', '1', '2'] // Array-like object const obj =  0: "a", 1: "b", 2: "c" >; console.log(Object.keys(obj)); // ['0', '1', '2'] // Array-like object with random key ordering const anObj =  100: "a", 2: "b", 7: "c" >; console.log(Object.keys(anObj)); // ['2', '7', '100'] // getFoo is a non-enumerable property const myObj = Object.create( >,  getFoo:  value()  return this.foo; >, >, >, ); myObj.foo = 1; console.log(Object.keys(myObj)); // ['foo'] 

If you want all string-keyed own properties, including non-enumerable ones, see Object.getOwnPropertyNames() .

Using Object.keys() on primitives

Non-object arguments are coerced to objects. Only strings may have own enumerable properties, while all other primitives return an empty array.

// Strings have indices as enumerable own properties console.log(Object.keys("foo")); // ['0', '1', '2'] // Other primitives have no own properties console.log(Object.keys(100)); // [] 

Note: In ES5, passing a non-object to Object.keys() threw a TypeError .

Specifications

Browser compatibility

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See also

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Getting JavaScript Object key List

Getting the list of keys of an object is a fundamental operation when working with JavaScript objects. There are many situations where developers need to get the list of keys, such as to check if a particular property exists in an object, to access a property of an object dynamically, to iterate over all the properties of an object, and so on.

This post will describe the methods to get the key list of an object.

How to Get the JavaScript Object key List?

For getting the list of keys of an object, use the following methods:

Method 1: Getting JavaScript Object key List Using “Object.keys()” Method

Use the JavaScript pre-built “Object.keys()” method to get the list of keys of the object. This method gives an array of all the enumerable property names (keys) of a given object.

Syntax
Use the following syntax for the Object.keys() method:

Example
Create an object named “obj” with three properties and their respective values:

Call the “Object.keys()” method to get the list of the keys of an object and store it in a variable “objKeyList”:

Print the list of the keys of an object on the console:

The output displays the array of keys of an object:

Method 2: Getting JavaScript Object key List Using “for-in” Loop with “push()” Method

You can also use the “for-in” loop to iterate the keys in an object and push the keys to an empty array using the “push()” method.

Example
Create an empty array named “objKeyList”:

Iterate the object using the “for-in” loop and push keys in an empty array with the help of the “push()” method:

Finally, print the array on the console:

Output

We have compiled all the essential information relevant to getting the list of keys of an object in JavaScript.

Conclusion

For getting the list of keys of an object, use the JavaScript pre-built “Object.keys()” method or the “for-in” loop with the “push()” method. The Object.keys() method gives an array of keys of the object. The for-in loop iterates the array keys and pushes them into an empty array. This post described the methods to get the key list of an object.

About the author

Farah Batool

I completed my master’s degree in computer science. I am an academic researcher and love to learn and write about new technologies. I am passionate about writing and sharing my experience with the world.

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