看起来没啥难度啊，不知道你是哪里搞不懂？不如把你的代码贴出来分析下

es6 语法

const convert = (() => {
    var rules = [
        [/&/g, "&"],
        [/</g, "&lt;"],
        [/>/g, "&gt;"],
        [/"/g, "&quot;"],
        [/'/g, "&apos;"]
    ];

    return function(s) {
        return rules.reduce((s, rule) => {
            return s.replace(rule[0], rule[1]);
        }, s);
    };
})();

// testing
[
    "Dolce & Gabbana",
    "Hamburgers < Pizza < Taos",
    "Sixty > twelve",
    "Stuff in \"quotation marks\"",
    "Shindler's List",
    "<>",
    "abc"
].forEach(s => console.log(convert(s)));