CODEWITHSUNDEEP
javascriptnode.jsjson
Jishnu
Jishnu

Reputation: 474

Correct way to check for a key inside JSON object

I know there are different ways to check for a key inside a JSON object.

const person = {
  name: 'john',
  age: 25,
  isTeenager: false
}

if (person.name) {
  console.log('name exists')
}

if (person.hasOwnProperty('age')) {
  console.log('age exists')
}

if (Object.prototype.hasOwnProperty.call(person, 'isTeenager')) {
  console.log('isTeenager exists')
}

These all work fine, but which is the correct and most efficient way of doing this?

Upvotes: 0

Views: 97

Answers (3)

Astronomize
Astronomize

Reputation: 11

Performance wise, if(obj.value != undefined) would be the "best";

var perf = require("perf_hooks").performance;

var obj = {
  iExist: "hi"
};

var start = perf.now();
if(obj.iExist != undefined) { // changed from obj.iExist to obj.iExist != undefined because of potential problems with booleans.
}
var end = perf.now();
console.log("basic if: " + (end - start));

var start1 = perf.now();
if(obj.hasOwnProperty('iExist')) {
}
var end1 = perf.now();
console.log("hasOwnProperty : " + (end1 - start));

Output:

basic if: 0.06810665130615234
hasOwnProperty : 4.006890296936035

Hope this helps!

Upvotes: 1

Beingnin
Beingnin

Reputation: 2422

You can't always rely on truthy-falsy check as you mentioned in the first example. It will fail on boolean properties if the value is false

if (person.isTeenager) {
  console.log('key exists')
}
else{
  console.log('key not exists')
}

You will get falsy on this. So always use hasOwnProperty method

Upvotes: 0

Sandesh Mankar
Sandesh Mankar

Reputation: 699

  1. hasOwnProperty() is correct way to define.
  2. hasOwnProperty() method returns a boolean denoting whether the object has the defined property as its own property.
const person = {
  name: 'john',
  age: 25,
  isTeenager: false
}

if (person.hasOwnProperty('age')) {
  console.log('age exists')
}

Upvotes: 5

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