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Type Casting in JavaScript

Introduction

Type Casting, also called Type Conversion, is the process of converting a value from one data type to another.

JavaScript supports two types of type casting:

  1. Implicit Type Casting (Automatic Conversion)
  2. Explicit Type Casting (Manual Conversion)

1. Implicit Type Casting

Implicit Type Casting is automatically performed by JavaScript whenever different data types are used together in an expression.

Example

var result = "The answer is: " + 42;

console.log(result);
console.log(typeof(result));

Output

The answer is: 42
string

Explanation

  • Here "The answer is: " is a string.
  • 42 is a number.
  • JavaScript automatically converts 42 into a string.
  • Then both values are concatenated.

This process is called Implicit Type Casting.

2. Explicit Type Casting

Explicit Type Casting means converting a value manually using built-in functions.

Some commonly used conversion functions are:

  • Number()
  • String()
  • Boolean()
  • parseInt()
  • parseFloat()

Example

var str = "123";

var num = Number(str);

console.log(num);
console.log(typeof(num));


var num2 = 456;

var str2 = String(num2);

console.log(str2);
console.log(typeof(str2));

Output

123
number

456
string

1. String to Number Conversion

You can convert a string into a number using:

  • Number()
  • parseInt()
  • parseFloat()

Example 1

var s = "Virat";

console.log(s);
console.log(typeof(s));

var s1 = Number(s);

console.log(s1);
console.log(typeof(s1));

Output

Virat
string

NaN
number

Explanation

  • "Virat" cannot be converted into a valid number.
  • Therefore Number() returns NaN.
  • NaN means Not a Number.

Example 2

var s2 = "v";

console.log(s2);
console.log(typeof(s2));

var s3 = Number(s2);

console.log(s3);
console.log(typeof(s3));

Output

v
string

NaN
number

Example 3

var s4 = "";

console.log(s4);
console.log(typeof(s4));

var s5 = Number(s4);

console.log(s5);
console.log(typeof(s5));

Output

""
string

0
number

Example 4

var s6 = " ";

console.log(s6);
console.log(typeof(s6));

var s7 = Number(s6);

console.log(s7);
console.log(typeof(s7));

Output

" "
string

0
number

2. Number to String Conversion

You can convert a Number to String using:

  • String()
  • toString()

Example 1

var age = 35;

console.log(age);
console.log(typeof(age));

var str = String(age);

console.log(str);
console.log(typeof(str));

Output

35
number

35
string

Example 2

var marks = 97.5;

console.log(marks);
console.log(typeof(marks));

var str2 = String(marks);

console.log(str2);
console.log(typeof(str2));

Output

97.5
number

97.5
string

Note:

Use String() with a capital S.

string() is incorrect and will throw an error.

3. String to Boolean Conversion

You can convert a String into Boolean using:

Boolean()

Rule

  • Non-empty String → true
  • Empty String → false

Example 1

var sa = "Sachin";

console.log(sa);
console.log(typeof(sa));

var sb = Boolean(sa);

console.log(sb);
console.log(typeof(sb));

Output

Sachin
string

true
boolean

Example 2

var s1 = "";

console.log(s1);
console.log(typeof(s1));

var s2 = Boolean(s1);

console.log(s2);
console.log(typeof(s2));

Output

""
string

false
boolean

4. Boolean to String Conversion

You can convert Boolean into String using:

  • String()
  • toString()

Example 1

var s1 = true;

console.log(s1);
console.log(typeof(s1));

var s2 = String(s1);

console.log(s2);
console.log(typeof(s2));

Output

true
boolean

true
string

Example 2

var s1 = false;

console.log(s1);
console.log(typeof(s1));

var s2 = String(s1);

console.log(s2);
console.log(typeof(s2));

Output

false
boolean

false
string

5. Boolean to Number Conversion

You can convert Boolean into Number using:

Number()

Rule

Boolean Number
true 1
false 0

Example 1

var s1 = true;

console.log(s1);
console.log(typeof(s1));

var s2 = Number(s1);

console.log(s2);
console.log(typeof(s2));

Output

true
boolean

1
number

Example 2

var s1 = false;

console.log(s1);
console.log(typeof(s1));

var s2 = Number(s1);

console.log(s2);
console.log(typeof(s2));

Output

false
boolean

0
number

6. Number to Boolean Conversion

You can convert Number into Boolean using:

Boolean()

Rule

Number Boolean
0 false
Any Non-Zero Number true

Example 1

var s1 = 42;

console.log(s1);
console.log(typeof(s1));

var s2 = Boolean(s1);

console.log(s2);
console.log(typeof(s2));

Output

42
number

true
boolean

Example 2

var s1 = 0;

console.log(s1);
console.log(typeof(s1));

var s2 = Boolean(s1);

console.log(s2);
console.log(typeof(s2));

Output

0
number

false
boolean

Important Notes

  1. Type Casting is the conversion of one data type into another.

  2. JavaScript supports:

    • Implicit Type Casting
    • Explicit Type Casting

  3. Number() converts values into numbers.

  4. String() converts values into strings.

  5. Boolean() converts values into booleans.

  6. NaN means Not a Number.

  7. Empty string "" converts to 0 using Number().

  8. Empty string "" converts to false using Boolean().

  9. Any non-zero number converts to true.

  10. true → 1 and false → 0 when converted to Number.

Summary

Type Casting is one of the most important concepts in JavaScript.

JavaScript allows:

  • String ↔ Number
  • String ↔ Boolean
  • Number ↔ String
  • Number ↔ Boolean
  • Boolean ↔ Number
  • Boolean ↔ String

Understanding Type Casting helps developers avoid unexpected results and write reliable JavaScript programs.