Type Coercion

Type coercion is the modification of a type within an expression in order to yield a result. In JavaScript expressions of mixed types are evaluated by default through type coercion. When strict type comparisons are required they should be implemented with the === and !== operators.

JavaScript is a relatively permissive language, and in many situations, such as mixed type expressions or function arguments the default behavior is to return a value, rather than an error.

Mixed Type Expressions

Expressions of mixed types are evaluated by changing one of the elements to match the other. For example, in the code below the string 6 is changed to a number type and will yield true and the product 36. However, the use of values that have been evaluated in such an expression may lead to unintended results when this behavior is not expected. It is a best practice to use the alternative, strict comparison operators to avoid errors from this form of evaluation.

console.log(6 == '6');
console.log(6 * '6');

console.log(6 === '6');

The code above will output:

true
36
false