diff --git a/1-js/05-data-types/02-number/article.md b/1-js/05-data-types/02-number/article.md
index 3f95c2ed..ea4a1f3b 100644
--- a/1-js/05-data-types/02-number/article.md
+++ b/1-js/05-data-types/02-number/article.md
@@ -432,6 +432,11 @@ For different numeral systems:
 - `parseInt(str, base)` parses the string `str` into an integer in numeral system with given `base`, `2 ≤ base ≤ 36`.
 - `num.toString(base)` converts a number to a string in the numeral system with the given `base`.
 
+For regular number tests:
+
+- `isNaN(value)` converts its argument to a number and then tests it for being `NaN`
+- `isFinite(value)` converts its argument to a number and returns `true` if it's a regular number, not `NaN/Infinity/-Infinity`
+
 For converting values like `12pt` and `100px` to a number:
 
 - Use `parseInt/parseFloat` for the "soft" conversion, which reads a number from a string and then returns the value they could read before the error.