Check if a Value is an Object using JavaScript

Check if a Value is an Object in JavaScript #

To check if a value is an object:

Verify the value has a type of object - typeof variable === 'object'.
Verify the value is not null - variable !== null.
Verify the value is not an array - !Array.isArray(variable).
If all conditions pass, the value is an object.

index.js

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const variable = {name: 'Tom'};

if (
  typeof variable === 'object' &&
  variable !== null &&
  !Array.isArray(variable)
) {
  // 👇️ this runs
  console.log('✅ Value is an object');
} else {
  console.log('⛔️ Value is not an object');
}

We used the logical AND (&&) operator to chain 3 conditions in a single if statement.

All conditions have to pass for the if block to run.

The first condition uses the typeof operator to check if a value has a type of "object".

The typeof operator returns a string that indicates the type of a value. Here are some examples.

index.js

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console.log(typeof {}); // 👉️ "object"
console.log(typeof []); // 👉️ "object"
console.log(typeof null); // 👉️ "object"
console.log(typeof function () {}); // 👉️ "function"
console.log(typeof (() => {})); // 👉️ "function"
console.log(typeof ''); // 👉️ "string"
console.log(typeof 0); // 👉️ "number"

Notice that an array and a null value also have a type of "object". To make sure the value doesn't store an array or null, we have to add 2 additional checks.

Our second condition checks that the value is not equal to null.

index.js

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const variable = {name: 'Tom'};

if (
  typeof variable === 'object' &&
  variable !== null &&
  !Array.isArray(variable)
) {
  // 👇️ this runs
  console.log('✅ Value is an object');
} else {
  console.log('⛔️ Value is not an object');
}

And the third condition checks that the value is not an array.

If all of the conditions are satisfied, the value is an object.

All of the following 3 values have a type of object:

an object literal {}
an array []
a null value

An alternative approach is to use the prototype property on the Object type.

index.js

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// 👇️ true
console.log(Object.prototype.toString.call({}) === '[object Object]');

// 👇️ false
console.log(Object.prototype.toString.call([]) === '[object Object]');

// 👇️ false
console.log(Object.prototype.toString.call(null) === '[object Object]');

We called to toString() method on the prototype, passing it an object, an array and null.

The names of all 3 are different when stringified:

index.js

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// 👇️️ "[object Object]"
console.log(Object.prototype.toString.call({}));

// 👇️ "[object Array]"
console.log(Object.prototype.toString.call([]));

// ️👇️ "[object Null]"
console.log(Object.prototype.toString.call(null));

This makes it a viable solution because we don't have to chain 3 conditions to get the result. However, I still prefer the first approach because it is more readable and intuitive.

It's best to avoid hardcoded strings like [object Object], because they leak implementation details, they are prone to errors and are difficult to debug.

Check if a Value is an Object using JavaScript

Check if a Value is an Object in JavaScript #

Further Reading #

Borislav Hadzhiev