5 Quick Ways to Check If Key Exists in JavaScript

In JavaScript, objects and maps are commonly used to store data as key-value pairs. There are several ways to check if a key exists in these data structures. This tutorial will guide you through five quick methods.

in Operator

The in operator checks if a property is in an object. It returns true if the property is found, false otherwise.

1var obj = { key1: "value1" };
2console.log("key1" in obj); // returns true
3console.log("key2" in obj); // returns false

hasOwnProperty()

The hasOwnProperty() method also checks if a property is in an object. Unlike the in operator, it doesn't check the prototype chain.

1var obj = { key1: "value1" };
2console.log(obj.hasOwnProperty("key1")); // returns true
3console.log(obj.hasOwnProperty("key2")); // returns false

Object.keys()

The Object.keys() method returns an array of an object's own property names. You can use the includes() method to check if a key exists.

1var obj = { key1: "value1" };
2console.log(Object.keys(obj).includes("key1")); // returns true
3console.log(Object.keys(obj).includes("key2")); // returns false

Object.getOwnPropertyNames()

The Object.getOwnPropertyNames() method returns an array of all properties found directly upon a given object. You can also use includes() to check for a key.

1var obj = { key1: "value1" };
2console.log(Object.getOwnPropertyNames(obj).includes("key1")); // returns true
3console.log(Object.getOwnPropertyNames(obj).includes("key2")); // returns false

Map.has()

The Map.has() method checks if an element with the specified key exists in a Map object.

1var map = new Map();
2map.set("key1", "value1");
3console.log(map.has("key1")); // returns true
4console.log(map.has("key2")); // returns false

For more JavaScript tutorials and tips, check out our Learn JavaScript course.

External Resources:

• MDN Web Docs - Keyed collections
• JavaScript Info - Map and Set
• W3Schools - JavaScript Objects