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TypeScript InstanceType<Type> Utility Type

JavaScript Type Conversion

Last Updated : 01 Feb, 2025

In JavaScript Type Conversion can be defined as converting the data type of the variables from one type to the other manually by the programmer(explicitly) or automatically by the JavaScript(implicitly).

Implicit Type Conversion (Coercion): Implicit Type Conversion occurs automatically by the JavaScript.
Explicit Type Conversion: Explicit Type Conversion occurs when the programmer manually changes the type of the variables using the function Number(), String(), and Boolean().

Implicit Type Conversion (Coercion)

In JavaScript, the implicit type conversion or coercion conversion can be defined as the automatic conversion of the data type of the variables from one type to another type. Implicit type conversion mostly occurs when we are performing the arithmetic or the logical operations.

String + Number (Concatenation)

When we add a string with the number, the JavaScript automatically converts the number into a string and performs string concatenation.

JavaScript

let res = 5 + "5"; console.log(res);

Output

Boolean to Number

When we perform the mathematical operations, then JavaScript automatically converts true to 1 and false to 0.

JavaScript

let res = true + 1; console.log(res);

Output

Equality Comparison (`==`)

When we use the equality operator in the JavaScript, it compares them after converting the value into the same data type.

JavaScript

let res = (5 == "5"); console.log(res);

Output

true

Automatic Conversion in Logical Operations

In JavaScript, these values are automatically converts undefined, null, “” (empty string), false, NaN, and 0 to false, and all other values to true.

JavaScript

let res = Boolean(""); let res2 = Boolean("Hello"); console.log(res) console.log(res2)

Output

false true

Explicit Type Conversion

In JavaScript, explicit type conversion can be defined as when we manually change the data type of the variable from one to other using some built-in JavaScript functions. JavaScript provides us the built-in functions for performing the explicit conversion.

Converting to String

In JavaScript, we can convert the value into a string using the String() function, toString(), and by concatenating the empty string.

JavaScript

let n = 123; let s1 = String(n); let s2 = n.toString(); console.log(s1) console.log(s2)

Output

123 123

Converting to Number

In JavaScript, we can convert the value into a number using the Number() function, parseInt(), and parseFloat().

JavaScript

let s = "123"; let n = Number(s); let s1 = "12.34"; let n1 = parseFloat(s1); console.log(n) console.log(n1)

Output

123 12.34

Converting to Boolean

In JavaScript, we can convert the value into a boolean we can use the Boolean() function.

JavaScript

let str = "Hello"; let b1 = Boolean(str);   let emptyStr = ""; let b2 = Boolean(emptyStr);   console.log(b1) console.log(b2)

Output

true false

Why Learn JavaScript Type Conversion?

Data Handling: In JavaScript when we are working with API responses, user inputs and calculations, these type of the operation require type conversion.
Prevent Bugs: It is important to understand the type conversion which can help in preventing bugs which occurs when JavaScript implicitly converts value.
Code Clarity: By performing the explicit conversion makes our code bug free and more clear.

JavaScript Type Conversion Comparison

Conversion Type	Implicit Conversion (Coercion)	Explicit Conversion
String + Number	Automatically converts numbers to strings	Manually convert using String() or .toString()
Number + Boolean	Converts true to 1 and false to 0	Use Number() to explicitly convert
String to Boolean	Non-empty strings convert to true, empty to false	Use Boolean() for clarity
Number from String	Implicit coercion with + operator	Use Number(), parseInt(), or parseFloat()

TypeScript InstanceType<Type> Utility Type

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