i18n-js/src/helpers/interpolate.ts

A small library to provide I18n on JavaScript.

import { TranslateOptions } from "../typing";
import { I18n } from "../I18n";
import { isSet } from "./isSet";

/**
 * This function interpolates the all variables in the given message.
 *
 * @private
 *
 * @param {I18n} i18n The I18n instance.
 *
 * @param {string} message The string containing the placeholders.
 *
 * @param {object} options The source object that will be used as the
 * placeholders' source.
 *
 * @returns {string} The interpolated string.
 */
export function interpolate(
  i18n: I18n,
  message: string,
  options: TranslateOptions,
): string {
  options = Object.keys(options).reduce((buffer, key) => {
    buffer[i18n.transformKey(key)] = options[key];
    return buffer;
  }, {} as TranslateOptions);
  const matches = message.match(i18n.placeholder);

  if (!matches) {
    return message;
  }

  while (matches.length) {
    let value: string;
    const placeholder = matches.shift() as string;
    const name = placeholder.replace(i18n.placeholder, "$1");

    if (isSet(options[name])) {
      value = options[name].toString().replace(/\$/gm, "_#$#_");
    } else if (name in options) {
      value = i18n.nullPlaceholder(i18n, placeholder, message, options);
    } else {
      value = i18n.missingPlaceholder(i18n, placeholder, message, options);
    }

    const regex = new RegExp(
      placeholder.replace(/\{/gm, "\\{").replace(/\}/gm, "\\}"),
      "g",
    );

    message = message.replace(regex, value);
  }

  return message.replace(/_#\$#_/g, "$");
}