Type coercion

{{GlossarySidebar}} 

Type coercion is the automatic or implicit conversion of values from one data type to another (such as strings to numbers). {{Glossary("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.

Examples

const value1 = "5";
const value2 = 9;
let sum = value1 + value2;

console.log(sum);

In the above example, JavaScript has coerced the 9 from a number into a string and then concatenated the two values together, resulting in a string of 59. JavaScript had a choice between a string or a number and decided to use a string.

The compiler could have coerced the 5 into a number and returned a sum of 14, but it did not. To return this result, you’d have to explicitly convert the 5 to a number using the {{jsxref("Global_Objects/Number", "Number()")}}  method:

sum = Number(value1) + value2;

See also

• Type conversion (Wikipedia)
• Related glossary terms:
  • {{Glossary("Type")}} 
  • {{Glossary("Type conversion")}}