polyfill.js

if (typeof Object.assign != 'function') {
    (function () {
        Object.assign = function (target) {
            'use strict';
            // 우리는 반드시 특정한 케이스에 대해서 확인해야 합니다.
            if (target === undefined || target === null) {
                throw new TypeError('Cannot convert undefined or null to object');
            }

            var output = Object(target);
            for (var index = 1; index < arguments.length; index++) {
                var source = arguments[index];
                if (source !== undefined && source !== null) {
                    for (var nextKey in source) {
                        if (source.hasOwnProperty(nextKey)) {
                            output[nextKey] = source[nextKey];
                        }
                    }
                }
            }
            return output;
        };
    })();
}

if (!Array.prototype.find) {
    Array.prototype.find = function(predicate) {
        if (this == null) {
            throw new TypeError('Array.prototype.find called on null or undefined');
        }
        if (typeof predicate !== 'function') {
            throw new TypeError('predicate must be a function');
        }
        var list = Object(this);
        var length = list.length >>> 0;
        var thisArg = arguments[1];
        var value;

        for (var i = 0; i < length; i++) {
            value = list[i];
            if (predicate.call(thisArg, value, i, list)) {
                return value;
            }
        }
        return undefined;
    };
}

Number.isInteger = Number.isInteger || function(value) {
    return typeof value === "number" &&
        isFinite(value) &&
        Math.floor(value) === value;
};

if (!Array.prototype.findIndex) {
    Object.defineProperty(Array.prototype, 'findIndex', {
        value: function(predicate) {
            'use strict';
            if (this == null) {
                throw new TypeError('Array.prototype.findIndex called on null or undefined');
            }
            if (typeof predicate !== 'function') {
                throw new TypeError('predicate must be a function');
            }
            var list = Object(this);
            var length = list.length >>> 0;
            var thisArg = arguments[1];
            var value;

            for (var i = 0; i < length; i++) {
                value = list[i];
                if (predicate.call(thisArg, value, i, list)) {
                    return i;
                }
            }
            return -1;
        },
        enumerable: false,
        configurable: false,
        writable: false
    });
}

(function (arr) {
    arr.forEach(function (item) {
        if (item.hasOwnProperty('remove')) {
            return;
        }
        Object.defineProperty(item, 'remove', {
            configurable: true,
            enumerable: true,
            writable: true,
            value: function remove() {
                if (this.parentNode !== null) this.parentNode.removeChild(this);
            }
        });
    });
})([Element.prototype, CharacterData.prototype, DocumentType.prototype]);