Convert Suffix to Key-Value Pair in JavaScript

Overview

Converting suffix notation (like chemical formulas) to key-value pairs involves parsing a string where elements are followed by optional numeric suffixes, and creating an object mapping each element to its count. This pattern is useful for parsing formulas, expressions, and structured strings.

Basic Implementation

/**
 * Convert chemistry elements into JSON objects
 * Basically chemistry elements suffix into key value pair
 * @param {string} formula
 * @returns {object} JSON object
 */
function convertToJSON(formula) {
  const elementCounts = {};
  let i = 0;

  while (i < formula.length) {
    const element = formula[i];
    i++;

    // Parse the number after the element, if any
    let countStr = "";
    while (i < formula.length && !isNaN(formula[i])) {
      countStr += formula[i];
      i++;
    }

    const count = countStr === "" ? 1 : parseInt(countStr);

    if (element in elementCounts) {
      elementCounts[element] += count;
    } else {
      elementCounts[element] = count;
    }
  }

  return elementCounts;
}

// Examples
console.log(convertToJSON("H2O"));      // {H: 2, O: 1}
console.log(convertToJSON("C6H12"));    // {C: 6, H: 12}
console.log(convertToJSON("COOH"));     // {C: 1, O: 2, H: 1}
console.log(convertToJSON("CH3COOH"));  // {C: 2, H: 4, O: 2}

Enhanced Implementation

With Multi-Character Elements

function parseFormula(formula) {
  const counts = {};
  let i = 0;
  
  while (i < formula.length) {
    // Parse element (one or two characters)
    let element = formula[i];
    i++;
    
    // Check for second lowercase letter (e.g., "Ca", "Fe")
    if (i < formula.length && /[a-z]/.test(formula[i])) {
      element += formula[i];
      i++;
    }
    
    // Parse number
    let numStr = '';
    while (i < formula.length && /\d/.test(formula[i])) {
      numStr += formula[i];
      i++;
    }
    
    const count = numStr === '' ? 1 : parseInt(numStr);
    counts[element] = (counts[element] || 0) + count;
  }
  
  return counts;
}

Use Cases

1. Chemical Formulas

const water = parseFormula("H2O");
const glucose = parseFormula("C6H12O6");

2. Expression Parsing

function parseExpression(expr) {
  // Similar pattern for parsing expressions
}

Best Practices

1. Handle Edge Cases: Empty strings, invalid formats
2. Validate Input: Check format before parsing
3. Support Multi-Char: Handle multi-character elements
4. Error Handling: Provide meaningful errors