The Infra Living Standard defines five characters as "ASCII whitespace": U+0009 TAB, U+000A LF, U+000C FF, U+000D CR, and U+0020 SPACE.

The ECMAScript Language Specification defines several Unicode code points as "white space": U+0009 CHARACTER TABULATION <TAB >, U+000B LINE TABULATION <VT >, U+000C FORM FEED <FF >, U+0020 SPACE <SP >, U+00A0 NO-BREAK SPACE <NBSP >, U+FEFF ZERO WIDTH NO-BREAK SPACE <ZWNBSP >, and any other Unicode "Space_Separator" code points <USP >.

• Whitespace character (Wikipedia)
• How whitespace is handled by HTML, CSS, and in the DOM
• white-space
• Specifications
  • ASCII whitespace spec
  • ECMAScript Language Specification
• Glossary
  1. Character