read-excel-file/modules/types/String.js

Read small to medium `*.xlsx` files in a browser or Node.js. Parse to JSON with a strict schema.

import InvalidError from './InvalidError.js';
export default function StringType(value) {
  if (typeof value === 'string') {
    return value;
  }
  // Excel tends to perform a forced automatic convertion of string-type values
  // to number-type ones when the user has input them. Otherwise, users wouldn't
  // be able to perform formula calculations on those cell values because users
  // won't bother manually choosing a "numeric" cell type for each cell, and
  // even if they did, choosing a "numeric" cell type every time wouldn't be an
  // acceptable "user experience".
  //
  // So, if a cell value is supposed to be a string and Excel has automatically
  // converted it to a number, perform a backwards conversion.
  //
  if (typeof value === 'number') {
    if (isNaN(value)) {
      throw new InvalidError('invalid_number');
    }
    // The global `isFinite()` function filters out:
    // * NaN
    // * -Infinity
    // * Infinity
    //
    // All other values pass (including non-numbers).
    //
    if (!isFinite(value)) {
      throw new InvalidError('out_of_bounds');
    }
    return String(value);
  }
  throw new InvalidError('not_a_string');
}
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