class Split1 {  constructor(value) {    this.value = value;  }  [Symbol.split](string) {    var index = string.indexOf(this.value);    return this.value + string.substr(0, index) + "/"      + string.substr(index + this.value.length);  }}console.log('foobar'.split(new Split1('foo')));// expected output: "foo/bar"