I'm getting SCRIPT5045: Assignment to read-only properties is not allowed in strict mode in IE 11 (latest Chrome works fine) in reference to the line

A.doc.head = A.doc.getElementsByTagName('HEAD')[0];.

I'm confused on how to fix it. I've included what should be the relevant code below.

(function (win, doc, arg) {

    'use strict';

    var A = win[arg.prefix] = {

        'win': win,

        'doc': doc,

        'arg': arg,

        'stu': {},

        'fun': (function () {

            return {

                init: function () {

                    var scripts = A.doc.getElementsByTagName('SCRIPT'),

                        n = scripts.length,

                        i;

                    for (i = 0; i < n; i = i + 1) {

                        if (scripts[i].src.match(A.arg.src)) {

                            A.arg.script = scripts[i];

                            A.arg.options = A.fun.options();

                            break;

                        }

                    }

                    A.doc.head = A.doc.getElementsByTagName('HEAD')[0];

                    A.fun.structure();

                },

                // more functions

        }())

    };

    A.fun.init();

}(window, document, {

    'prefix': 'accescape_' + new Date().getTime(),

    'src': '/widget.js',

    'defaults': {

        'language': 'en'

    }

}));