5 Ways To Check If Property Exists In Javascript Object

Welcome to a quick tutorial on how to check if a property exists in a Javascript object. In an array, we can conveniently use the includes function to check if a value exists. But in objects, things are a little different.

That covers the basics, but let us walk through more examples in this guide – Read on!

ⓘ I have included a zip file with all the example source code at the start of this tutorial, so you don’t have to copy-paste everything… Or if you just want to dive straight in.

 

 

TLDR – QUICK SLIDES

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TABLE OF CONTENTS

 

 

QUICK NOTES

If you spot a bug, feel free to comment below. I try to answer short questions too, but it is one person versus the entire world… If you need answers urgently, please check out my list of websites to get help with programming.

 

EXAMPLE CODE DOWNLOAD

Click here to download the source code, I have released it under the MIT license, so feel free to build on top of it or use it in your own project.

 

 

 

1) HAS OWN PROPERTY

// (A) THE OBJECT
var obj = { 
  Name: "Joa Doe", 
  Email: "joa@doe.com",
  Gender: "Female"
};
 
// (B) CHECK PROPERTY EXIST
console.log(obj.hasOwnProperty("Name")); // true
console.log(obj.hasOwnProperty("Foo")); // false

As in the introduction above, the OBJECT.hasOwnProperty(KEY) function is one of the easiest methods to check if a property exists. But please take note – This function will only go 1 level deep and does not “dig” into nested objects.

 

2) EXTRACT KEYS & INCLUDES

// (A) THE OBJECT
var obj = { 
  Name: "Job Doe", 
  Email: "job@doe.com",
  Gender: "Male"
};

// (B) GET KEYS
var keys = Object.keys(obj);
console.log(keys); // ["Name", "Email", "Gender"]

// (C) CHECK PROPERTY EXIST
console.log(keys.includes("Email")); // true
console.log(keys.indexOf("Gender")); // 2, will return -1 if not found

This is the roundabout way to first extract all the keys of the object using Object.keys(OBJECT) first, then use either includes(KEY) or indexOf(KEY) to check if a property exists.

 

 

3) IN OPERATOR

// (A) THE OBJECT
var obj = { 
  Name: "Joe Doe", 
  Email: "joe@doe.com",
  Gender: "Male"
};

// (B) CHECK PROPERTY EXIST
console.log("Name" in obj); // true
console.log("FOO" in obj); // false

Yep, this should be self-explanatory. This is kind of the alternate way to do hasOwnProperty().

 

4) COMPARISON OPERATOR

// (A) THE OBJECT
var obj = { 
  Name: "Joi Doe", 
  Email: "joi@doe.com",
  Gender: "Female"
};

// (B) CHECK PROPERTY EXIST
console.log(obj["Name"] !== undefined); // true
console.log(obj["Foo"] !== undefined); // false

As you guys already know, we can use either OBJECT[KEY] or OBJECT.KEY to access the values in the object. So when OBJECT[KEY] === undefined, we can kind of assume that the key does not exist. Take extra note though, this method is not 100% accurate. We can manually define OBJECT[KEY] = undefined or OBJECT[KEY] = null.

 

 

5) MANUAL LOOP & CHECK

// (A) THE OBJECT
var obj = { 
  Name: "Jon Doe", 
  Email: "jon@doe.com",
  Gender: "Male"
};
 
// (B) MANUAL LOOP & CHECK
var check = "Email", exist = false;
for (let key in obj) { if (key == check) {
  exist = true;
  break;
}}
console.log(exist); // true

I know, the trolls are going to say “manual loop is so dumb and useless”. Well, let us not discount that there may still be other possible uses for it. Maybe replace the value if the key matches a search pattern, or even count the total number of instances along the way.

var count = 0;
for (let key in obj) { if (KEY MATCHES SEARCH PATTERN) {
  obj[key] = "FOO!";
  count++;
}}

 

6) CHECKING NESTED OBJECTS

The dreaded nested objects… Just a quick recap:

• hasOwnProperty() will not work well, only goes 1 level deep.
• Object.keys() will not work well, only goes 1 level deep.
• KEY in OBJECT will also not work well, only goes 1 level deep.

So just how do we check if a property exists in a nested object? The only way is to create a recursive function to extract all the keys.

// (A) THE OBJECT
var obj = { 
  Name: "Joy Doe", 
  Email: "joy@doe.com",
  Gender: "Female",
  Fav: {
    Colors: ["Red", "Green", "Blue"],
    Foods: ["Pizza", "Spam", { Foo: "Bar" }]
  }
};

// (B) RECURSIVE FUNCTION TO DIG OUT ALL KEYS
var flatval = value => {
  let temp = [];
  if (typeof value == "object") {
    if (Array.isArray(value)) { for (let i of value) {
      if (typeof i == "object") { temp = temp.concat(flatval(i)); }
    }} else {
      temp = temp.concat(Object.keys(value));
      for (let i of temp) { if (typeof value[i] == "object") {
          temp = temp.concat(flatval(value[i]));
      }}
    }
  }
  return temp;
};
var flattened = flatval(obj);
console.log(flattened);

// (C) FINALLY, JUST CHECK AS USUAL
console.log(flattened.includes("Foo")); // true
console.log(flattened.indexOf("Colors")); // 4

Yep. It’s painful, but it works.

 

 

 

SUMMARY

Function/Statement	Description	Reference Link
OBJECT.hasOwnProperty(KEY)	Check if the object has the given key.	Click Here
Object.keys(OBJECT)	Return all the keys of the given object. Note, 1 level only.	Click Here
ARRAY.includes(VALUE)	Check if the given value exists in the array.	Click Here
ARRAY.indexOf(VALUE)	Returns the index of the given value, -1 if not found	Click Here
KEY in OBJECT	Checks if the given key is in the object. Note, 1 level only.	Click Here
OBJECT[KEY] !== undefined	Checks if the given key is defined in the object.	Click Here

 

LINKS & REFERENCES

• How To Check If Value Exists In Javascript Object – Code Boxx
• Checking if a key exists in a JavaScript object? – StackOverflow
• How to check a key exists in JavaScript object? – GeeksForGeeks

 

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