Unknown code on my site - Copyright The Closure Library Authors. SPDX-License-Identifier: Apache-2.0

[datalocks]

The following code is on my clients website and is causing an iFrame with 'NF' to appear at the top of one of our pages. What is this code and what is it supposed to do?
I am unsure where this code has been added to the site as well, i have checked website source code and GTM.

(function() {
    /*

 Copyright The Closure Library Authors.
 SPDX-License-Identifier: Apache-2.0
*/
    'use strict';
    var e = class {
        constructor(c) {
            this.g = d;
            this.h = c;
            this.g.document.addEventListener("__TAG_ASSISTANT_API_MESSAGE", b=>{
                b = b.detail;
                var a;
                if (a = this.receiver) {
                    a: if (a = null === b || void 0 === b ? void 0 : b.type,
                    "string" !== typeof a)
                        a = !1;
                    else
                        switch (a) {
                        case "PIPE_MESSAGE":
                        case "DISCONNECT":
                        case "API_INSTALLED":
                        case "WINDOWS_CLOSED":
                            a = !0;
                            break a;
                        default:
                            a = !1
                        }
                    if (a)
                        a: if (a = null === b || void 0 === b ? void 0 : b.source,
                        "string" !== typeof a)
                            a = !1;
                        else
                            switch (a) {
                            case "PAGE":
                            case "EXTENSION":
                                a = !0;
                                break a;
                            default:
                                a = !1
                            }
                }
                a && "PIPE_MESSAGE" === b.type && "EXTENSION" === b.source && this.receiver(b.data, b.origin)
            }
            );
            this.g.document.dispatchEvent(new CustomEvent("__TAG_ASSISTANT_API_MESSAGE",{
                detail: {
                    type: "API_INSTALLED",
                    source: "PAGE"
                }
            }))
        }
        setReceiver(c) {
            this.receiver = c
        }
        sendMessage(c) {
            this.g.document.dispatchEvent(new CustomEvent("__TAG_ASSISTANT_API_MESSAGE",{
                detail: {
                    type: "PIPE_MESSAGE",
                    source: "PAGE",
                    data: c,
                    origin: this.g.origin
                }
            }))
        }
        disconnect() {
            this.g.document.dispatchEvent(new CustomEvent("__TAG_ASSISTANT_API_MESSAGE",{
                detail: {
                    type: "DISCONNECT",
                    source: "PAGE"
                }
            }));
            this.h()
        }
    }
    ;
    const d = window;
    d.__TAG_ASSISTANT_API = d.__TAG_ASSISTANT_API || new e(()=>{
        d.__TAG_ASSISTANT_API = void 0
    }
    );
}
).call(this);

[12wrigja]

https://chrome.google.com/webstore/detail/tag-assistant-companion/jmekfmbnaedfebfnmakmokmlfpblbfdm

Do you have the Tag Assistant companion extension installed?