Type Coercion in JavaScript

Type Coercion is process of automatic or implicit conversion of value from one data type to another. Conversion from Number to String , String to Number, Boolean to Number and so on. Type coercion occurs when different types of operators are applied to the values

• Number to String

Anything added to string first JavaScript convert it into string and then concatenates both the strings.

Note : It occur only with "+" operator

// Number to String conversion
let a = 10 + "20"
let b = "10" + 20
let c = undefined + "20"
let d = true + "10-1"

console.log(a)  // 1020
console.log(b)  // 1020
console.log(c)  // undefined20
console.log(d)  // true10-1

• String to Number

When operation like subtraction( - ), multiplication( * ), division( / ), modulus (%) is performed first JavaScript convert it into number then apply these operations

Note : The string should be a Number

// String to Number
let a = "20" - 10
let b = "5" - 10
let c = "70-1" * 1
let d = "20" / 3
let e = "20" % 2

console.log(a) // 10
console.log(b) // -5
console.log(c) // NaN (not a number), how ? check the note
console.log(d) // 6.67 (approx)
console.log(e) // 0

• Boolean to Number

When a boolean is added to a Number, boolean value is converted to number as 0 for "false" and 1 for "true"

// Boolean to Number
let a = true + 10
let b = false + 10
let c = 10 * true
let d = 10 / false

console.log(a) // 11
console.log(b) // 10
console.log(c) // 10
console.log(d) // Infinity

• Equality Operator

The equality ( == ) is used to compare value irrespective of their type. This happen by coercion of Non-Number to Number data type

Note : To avoid type coercion, use the triple-equals operator ( === )

// Equality Operator
let a = ( 11 == "11" )
let b = ( false == 0 )
let c = ( true == 1 )
let d = ( true == "true" )
let e = ( true === 1 )  // To avoid type coercion

console.log(a) // true
console.log(b) // true
console.log(c) // true
console.log(d) // false
console.log(e) // false