@ungap/essential-map/cjs/index.js

An essential Map poorlyfill for legacy browsers.

/*! (c) Andrea Giammarchi - ISC */
var self = {};
try { self.Map = Map; }
catch (Map) {
  self.Map = function Map() {
    var i = 0;
    var k = [];
    var v = [];
    return {
      delete: function (key) {
        var had = contains(key);
        if (had) {
          k.splice(i, 1);
          v.splice(i, 1);
        }
        return had;
      },
      forEach: function forEach(callback, context) {
        k.forEach(
          function (key, i)  {
            callback.call(context, v[i], key, this);
          },
          this
        );
      },
      get: function get(key) {
        return contains(key) ? v[i] : void 0;
      },
      has: function has(key) {
        return contains(key);
      },
      set: function set(key, value) {
        v[contains(key) ? i : (k.push(key) - 1)] = value;
        return this;
      }
    };
    function contains(v) {
      i = k.indexOf(v);
      return -1 < i;
    }
  };
}
module.exports = self.Map;