lib/index.esm.js
function (COLLECTION) {
  _export(_export.S, COLLECTION, { of: function of() {
    var length = arguments.length;
    var A = new Array(length);
    while (length--) A[length] = arguments[length];
    return new this(A);
  } });
}
function (COLLECTION) {
  _export(_export.S, COLLECTION, { of: function of() {
    var length = arguments.length;
    var A = new Array(length);
    while (length--) A[length] = arguments[length];
    return new this(A);
  } });
}
https://tc39.github.io/proposal-setmap-offrom/