Function parseExpressionString

modules/json/src/helpers/parse-expression-string.ts:30–64

(
  propValue: string,
  configuration?
)

 * @returns A callable accessor compiled from the expression string.
 */
export function parseExpressionString(
  propValue: string,
  configuration?
): (row: Record<string, unknown>) => unknown {
  // NOTE: Can be null which represents invalid function. Return null so that prop can be omitted
  if (propValue in cachedExpressionMap) {
    return cachedExpressionMap[propValue];
  }

  let func;
  // Compile with expression-eval
  const ast = parse(propValue);
  if (ast.type === 'Identifier') {
    func = row => {
      return get(row, propValue);
    };
  } else {
    // NOTE: To avoid security risks, the arguments passed to the
    // compiled expression must only give access to pure data (no globals etc)
    // We disable function call syntax
    traverse(ast, node => {
      if (node.type === 'CallExpression') {
        throw new Error('Function calls not allowed in JSON expressions');
      }
    });
    // TODO Something like `expressionEval.eval(ast, {row});` would be useful for unpacking arrays
    func = row => {
      return evaluate(ast, row);
    };
  }

  // Cache the compiled function
  cachedExpressionMap[propValue] = func;
  return func;
}

/**
 * Recursively visits nodes in an expression AST.