How Can I Efficiently Retrieve a List of Object Property Names in JavaScript?

Identifying Object Properties in JavaScript

In JavaScript, objects play a crucial role in storing and manipulating data. To access the properties (key-value pairs) of an object, various methods are available. This article explores the efficient ways to retrieve a list of property names, which can be useful for a variety of purposes.

Object.keys Method

Modern browsers (IE9 , FF4 , Chrome5 , Opera12 , Safari5 ) provide the Object.keys method, which returns an array containing the property names of the specified object.

const myObject = {
  ircEvent: "PRIVMSG",
  method: "newURI",
  regex: "^http://.*"
};

const keys = Object.keys(myObject);
console.log(keys); // ["ircEvent", "method", "regex"]

Polyfill for Older Browsers

For browsers that don't support Object.keys, a polyfill can be used:

const getKeys = function(obj) {
   const keys = [];
   for (const key in obj) {
      keys.push(key);
   }
   return keys;
}

const keys = getKeys(myObject);
console.log(keys); // ["ircEvent", "method", "regex"]

Extend Object.prototype

Alternatively, the Object.prototype can be extended with a .keys() method:

Object.prototype.keys = function() {
   const keys = [];
   for (const key in this) {
      keys.push(key);
   }
   return keys;
}

const keys = myObject.keys();
console.log(keys); // ["ircEvent", "method", "regex"]

Note that extending the prototype may have unintended side effects. It's generally recommended to use Object.keys or a polyfill instead.

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