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Type Coercion

Type coercion is the automatic or implicit conversion of values from one data type to another (such as strings to numbers). Type conversion is similar to type coercion because they both convert values from one data type to another with one key difference — type coercion is implicit whereas type conversion can be either implicit or explicit.

1. Implicit Coercion

Implicit coercion happens when you apply operators to values of different types.

String Coercion

When the + operator is used with a string, it converts the other value to a string.

const x = 1 + "2"; // "12"
const y = "Hello " + 5; // "Hello 5"

Number Coercion

Mathematical operators other than + (like -, *, /, %) convert values to numbers.

const x = "5" - 2; // 3
const y = "10" * "2"; // 20
const z = "10" / 2; // 5

Boolean Coercion

Happens in logical contexts (like if statements) or with logical operators (||, &&, !).

Falsy Values:

  • false
  • 0
  • "" (empty string)
  • null
  • undefined
  • NaN

All other values are Truthy.

if ("hello") {
  console.log("This runs"); // "hello" is truthy
}

if (0) {
  console.log("This won't run"); // 0 is falsy
}

2. Explicit Coercion

Explicit coercion is when you manually convert types using built-in functions.

Number("123"); // 123
String(123); // "123"
Boolean(1); // true

3. Equality Operators (== vs ===)

  • Loose Equality (==): Performs type coercion before comparing.
    1 == "1"; // true
null == undefined; // true
  • Strict Equality (===): Does NOT perform type coercion. Types must match.
    1 === "1"; // false
null === undefined; // false

Best Practice: Always use === to avoid unexpected coercion bugs.

programming/javascript/vanilla/javascript programming/javascript/vanilla/data-types

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Created: March 17, 2026 • Last Modified: February 1, 2026