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JavaScript Academy · Lesson

Type Coercion: Safe Patterns to Avoid Surprises

Understand implicit vs explicit coercion; prefer clear casts with Number/String/Boolean; handle NaN safely.

Intro

Goal: See when JavaScript converts types, what results it produces, and how to use explicit casts to stay predictable.

  • Implicit vs explicit
  • Number/String/Boolean
  • NaN safety
Type Coercion: Safe Patterns to Avoid Surprises — illustration 1

Implicit coercion demo

+ with a string triggers concatenation; - and * try numeric conversion.

// Implicit coercion can surprise beginners
console.log("5" + 1);     
// "51"  (string concatenation)
console.log(5 + "1");    
// "51"  (number -> string)
console.log("5" - 1);     
// 4     (string -> number)
console.log("5" * 2);     
// 10    (string -> number)
Type Coercion: Safe Patterns to Avoid Surprises — illustration 2

All lessons in this course

  1. Primitives vs Objects & Core Types
  2. typeof, Truthy/Falsy, and == vs ===
  3. Type Coercion: Safe Patterns to Avoid Surprises
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