discord.js/src/structures/ReactionEmoji.js

/**
 * Represents a limited emoji set used for both custom and unicode emojis. Custom emojis
 * will use this class opposed to the Emoji class when the client doesn't know enough
 * information about them.
 */
class ReactionEmoji {
  constructor(reaction, name, id) {
    /**
     * The message reaction this emoji refers to
     * @type {MessageReaction}
     */
    this.reaction = reaction;

    /**
     * The name of this reaction emoji.
     * @type {string}
     */
    this.name = name;

    /**
     * The ID of this reaction emoji.
     * @type {string}
     */
    this.id = id;
  }

  /**
   * The identifier of this emoji, used for message reactions
   * @readonly
   * @type {string}
   */
  get identifier() {
    if (this.id) return `${this.name}:${this.id}`;
    return encodeURIComponent(this.name);
  }

  /**
   * Creates the text required to form a graphical emoji on Discord.
   * @example
   * // send the emoji used in a reaction to the channel the reaction is part of
   * reaction.message.channel.sendMessage(`The emoji used is ${reaction.emoji}`);
   * @returns {string}
   */
  toString() {
    return this.id ? `<:${this.name}:${this.id}>` : this.name;
  }
}

module.exports = ReactionEmoji;