Function formatFormula

formatFormula(formula: string): string

Formats a plain-ASCII chemical formula with proper Unicode notation: periods that join formula units become an adduct/hydrate dot (⋅), and atom-count digits become subscripts. Digits that are leading stoichiometric coefficients — those at the start of a unit, after a space, or right after the adduct dot — are left full-size, since their preceding character isn't an atom or bracket. Intended for formulas that arrive as plain text (no <sub> markup); tagged formulas should go through findFormulaInHtml instead.

Parameters

formula: string
A plain-ASCII formula, e.g. "C6H15NO3.5H3PO4"

Returns string

The formula with subscripted atom counts and adduct dots, e.g. "C₆H₁₅NO₃⋅5H₃PO₄"

Example

formatFormula("C6H15NO3")        // "C₆H₁₅NO₃"
formatFormula("C6H15NO3.H3PO4")  // "C₆H₁₅NO₃⋅H₃PO₄"
formatFormula("C6H15NO3.5H3PO4") // "C₆H₁₅NO₃⋅5H₃PO₄"
formatFormula("NaOH")            // "NaOH"

Source

export function formatFormula(formula: string): string {
  return (
    formula
      // 1. period(s) between formula units → adduct dot
      .replace(new RegExp(`(${TARGET_ADDUCT_DOTS.join('|')})`, 'g'), ADDUCT_DOT)
      // 2. a run of digits directly after an atom (letter), ) or ] → subscript.
      //    Digits after the start, a space, or the adduct dot are stoichiometric
      //    coefficients, so their preceding char isn't a letter/bracket → skipped.
      .replace(/(?<=[A-Za-z)\]])\d+/g, subscript)
  );
}