Table of Contents

Validations are the key things to prevent the application’s unexpected behaviour. This is a list of basic validations every nodejs developer should know about.
I will keep updating this article with new validation and best approaches.

typeof operator
- Syntax
Number check
- Check NaN (not a number)
- Check if the number is finite
String Check
Boolean Check
Undefined Check
Null Check
- Null check using the Object
Function check
Object Check
- Check using the instanceof
Array Check
Buffer Check
Conclusion

typeof operator #

Javascript provides a typeof operator. This operator returns the type of the variable.

Syntax #

typeof operand;
typeof operand;

Return Values of the typeof

Type	Return
Number	“number”
String	“string”
Boolean	“boolean”
Undefined	“undefined”
Null	“object”
Function	“function”
Object	“object”

There are a couple of other like BigInt(returns “bigint”) which introduced in ECMAScript 2020 and Symbol(returns “symbol”) which introduced in the ECMAScript 2015. Learn more

Number check #

For all the numbers(integer, floating) and Infinity, it returns number.

const num1 = 12;

// check if it is a number
if (typeof num1 === "number") {
  console.log("It is a number");
} else {
  console.log("It is not a number");
}

// check for Infinity
const num2 = Infinity;

// check if it is a number
if (typeof num2 === "number") {
  console.log("It is a number");
} else {
  console.log("It is not a number");
}

// check for string
const num3 = "2";

// check if it is a number
if (typeof num3 === "number") {
  console.log("It is a number");
} else {
  console.log("It is not a number");
}

Output

It is a number
It is a number
It is not a number

Check NaN (not a number) #

NaN is a property and its type is number. NaN is never equal to any number including NaN itself.

NaN != NaN

To check NaN, always use isNaN method.

const str = "js";

// check if it is not a number
if (isNaN(str)) {
  console.log("It is not a number");
} else {
  console.log("It is a number");
}

Output

It is not a number

Check if the number is finite #

isFinite method returns a boolean value if a number is finite or not.

const num1 = 12;

// check if finite
if (isFinite(num1)) {
  console.log("Number is finite");
} else {
  console.log("Number is not finite");
}

const num2 = Infinity;

// check if finite
if (isFinite(num2)) {
  console.log("Number is finite");
} else {
  console.log("Number is not finite");
}

Output

Number is finite
Number is not finite

String Check #

// check for string
const str = "2";

// check if it is a string
if (typeof str === "string") {
  console.log("It is a string");
} else {
  console.log("It is not a string");
}

Output

It is a string

Boolean Check #

// check for boolean
const bool = true;

// check if it is a boolean
if (typeof bool === "boolean") {
  console.log("It is a boolean");
} else {
  console.log("It is not a boolean");
}

// check for boolean
const str = "str";

// check if it is a boolean
if (typeof str === "boolean") {
  console.log("It is a boolean");
} else {
  console.log("It is not a boolean");
}

Output

It is a boolean
It is not a boolean

Undefined Check #

// check for undefined
const variable = undefined;

// check if it is undefined
if (typeof variable === "undefined") {
  console.log("It is undefined");
} else {
  console.log("It is not undefined");
}

Output

It is undefined

Null Check #

typeof null returns Object.

Check out why it returns Object.

// check for null
const variable = null;

// check if it is a null
if (variable === null) {
  console.log("It is a null");
} else {
  console.log("It is not a null");
}

Output

It is a null

Null check using the Object #

function isNull(variable) {
  return Object.prototype.toString.call(variable) === "[object Null]";
}

Function check #

// check for function
const variable = function (x, y) {
  return x + y;
};

// check if it is a function
if (typeof variable === "function") {
  console.log("It is a function");
} else {
  console.log("It is not a function");
}

Output

It is a function

Object Check #

There are multiple ways to check if the variable is an object or not.

// check for Object
const variable = {
  id: 12,
};

// check if it is an Object
if (typeof variable === "object") {
  console.log("It is an Object");
} else {
  console.log("It is not an Object");
}

Output

It is an Object

Note: null is also an object

Check the object and not null.

// check for Object and not null
const variable = {
  id: 12,
};

// check if it is an Object
if (typeof variable === "object" && variable !== null) {
  console.log("It is an Object and not null");
} else {
  console.log("It is not an Object");
}

Output

It is an Object and not null

Check using the instanceof #

The instanceof operator returns boolean, it checks if the variable has a prototype property of a constructor exists in the prototype chain of an object.

The instanceof operator also takes care of the null object. It returns false to null.

// check for Object
const variable = {
  id: 12,
};

// check if it is an Object
if (variable instanceof Object) {
  console.log("It is an Object");
} else {
  console.log("It is not an Object");
}

// check for Object
const variable2 = null;

// check if it is an Object
if (variable2 instanceof Object) {
  console.log("It is an Object");
} else {
  console.log("It is not an Object");
}

Output

It is an Object
It is not an Object

Array Check #

An array is also an Object. Using typeof requires multiple validations to validate it.

Empty array is a true value.

In javascript Array class is a global object that is used in the construction in the arrays.
Array class has many methods and one of them is isArray.

isArray returns true if the variable is an array else false.

// check for Array
const arr = ["hello", "world"];

// check if it is an Array
if (Array.isArray(arr)) {
  console.log("It is an Array");
} else {
  console.log("It is not an Array");
}

// check for Array
const arr2 = 12;

// check if it is an Array
if (Array.isArray(arr2)) {
  console.log("It is an Array");
} else {
  console.log("It is not an Array");
}

Output

It is an Array
It is not an Array

Other alternatives to check the array.

// conditions
1. arr.constructor === Array

2. arr instanceof Array

3. Object.prototype.toString.call(arr) === '[object Array]'

Buffer Check #

In the nodejs, Buffer class is in the global scope.
Buffer class has an isBuffer method to check if the variable is buffer or not.

Buffer objects are used to represent a fixed-length sequence of bytes. The Buffer class is a subclass of JavaScript’s Uint8Array class and extends it with methods that cover additional use cases. Node.js APIs accept plain Uint8Arrays wherever Buffers are supported as well.

// check for Buffer
const buf = Buffer.from("Hello World");

// check if it is a Buffer
if (Buffer.isBuffer(buf)) {
  console.log("It is a Buffer");
} else {
  console.log("It is not a Buffer");
}

Output

It is a Buffer

⚠️ Buffer class is not available in the Javascript. Don’t try it in client-side application it will throw an error.

Conclusion #

I’ll keep updating it with frequent validation a javascript or nodejs developer has to do every day.
Thanks for reading and please let me what else can be added in this.