JavaScript Type Coercion

Forced Coercion Cheatsheet

• Boolean
  • !!var
  • Boolean(var)
  • typeof(var) === 'boolean'
• Number
  • +var
  • Number(var)
  • Returns NaN if var contains non-numeric chars.
  • typeof(var) === 'number'
• String
  • String(var)
  • typeof(var) === 'string'

Required Reading

• JavaScript type coercion explained

Definition

• “Type coercion is the process of converting value from one type to another (such as string to number, object to boolean, and so on). Any type, be it primitive or an object, is a valid subject for type coercion. To recall, primitives are: number, string, boolean, null, undefined + Symbol (added in ES6).” - JavaScript type coercion explained

About ===

• Rule: Always use 3 equals unless you have a good reason to use 2.
• 3 == "3" //true
• 3 == "03" //true
• 3 === "3" //false
• In other words, === does not trigger type coercion.
• Insired by https://wtfjs.com/wtfs/2010-02-15-coerce-equality
• See also https://dorey.github.io/JavaScript-Equality-Table/