Ticket #30781: array-prototype-indexof-polyfill.php

<?php
/**
 * Plugin Name: Array.prototype.indexOf() polyfill for LTE IE8
 * Description: As reported in WordPress Trac #30781, an error is happening in WP4.1.0 for IE8 users due to that browser's incomplete implementation of modern JS methods.
 * Plugin URI: https://core.trac.wordpress.org/ticket/30781
 * Author: Weston Ruter, XWP
 * Author URI: https://xwp.co/
 */

/**
 * Via https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/indexOf
 */
function array_prototype_indexof_polyfill() {
        ?>
        <script>
        // Production steps of ECMA-262, Edition 5, 15.4.4.14
        // Reference: http://es5.github.io/#x15.4.4.14
        if (!Array.prototype.indexOf) {
                Array.prototype.indexOf = function(searchElement, fromIndex) {

                        var k;

                        // 1. Let O be the result of calling ToObject passing
                        //    the this value as the argument.
                        if (this == null) {
                                throw new TypeError('"this" is null or not defined');
                        }

                        var O = Object(this);

                        // 2. Let lenValue be the result of calling the Get
                        //    internal method of O with the argument "length".
                        // 3. Let len be ToUint32(lenValue).
                        var len = O.length >>> 0;

                        // 4. If len is 0, return -1.
                        if (len === 0) {
                                return -1;
                        }

                        // 5. If argument fromIndex was passed let n be
                        //    ToInteger(fromIndex); else let n be 0.
                        var n = +fromIndex || 0;

                        if (Math.abs(n) === Infinity) {
                                n = 0;
                        }

                        // 6. If n >= len, return -1.
                        if (n >= len) {
                                return -1;
                        }

                        // 7. If n >= 0, then Let k be n.
                        // 8. Else, n<0, Let k be len - abs(n).
                        //    If k is less than 0, then let k be 0.
                        k = Math.max(n >= 0 ? n : len - Math.abs(n), 0);

                        // 9. Repeat, while k < len
                        while (k < len) {
                                // a. Let Pk be ToString(k).
                                //   This is implicit for LHS operands of the in operator
                                // b. Let kPresent be the result of calling the
                                //    HasProperty internal method of O with argument Pk.
                                //   This step can be combined with c
                                // c. If kPresent is true, then
                                //    i.  Let elementK be the result of calling the Get
                                //        internal method of O with the argument ToString(k).
                                //   ii.  Let same be the result of applying the
                                //        Strict Equality Comparison Algorithm to
                                //        searchElement and elementK.
                                //  iii.  If same is true, return k.
                                if (k in O && O[k] === searchElement) {
                                        return k;
                                }
                                k++;
                        }
                        return -1;
                };
        }
        </script>
        <?php
}

add_action( 'customize_controls_print_scripts', 'array_prototype_indexof_polyfill', 1 );