Unique Terms

What’s Coercion?

Coercion is the term that is used for unexpected type casting in JavaScript. Often when you are working with data you will need to transform it from one data type to another — something that every developer does on a daily basis. Coercion refers to those not-obvious type casts that happen as a side-effect of different operations.

Strings and Numbers

42 + "0" // "420"

14 + "" // "14"

"42" - 7 // 35

"42" - 0 // 42

"42" - "9" // 33

["alex", "sam"] + ["jon", "mary"] // "alex,samjon,mary"

[3] - [1] // 2

["alex", "sam"] - ["jon", "mary"] // NaN

Booleans

const a = 100

const b = "test"

const c = null

a || b // 100

a && b // "test"

a || c // 100

a && c // null

b || c // "test"

b && c // null

Equality

42 == "42" // true

42 === "42" // false

https://hackernoon.com/understanding-js-coercion-ff5684475bfc