全部代码。

(function () {
    "use strict";
    const MAX_WIDTH = 540;
    const MIN_WIDTH = 375;

    //获取dpr
    let dpr = window.devicePixelRatio;
    dpr = Math.max(Math.round(dpr), 1);

    console.log(dpr);

    //处理Dpr
    handleDpr();

    //处理Rem
    handleRem();


    function handleDpr() {

        //dpr在移动设备中大小
        let mbDpr = 1 / dpr;

        //viewport content
        let content = `width=device-width,initial-scale=${mbDpr},minimum-scale=${mbDpr},maximum-scale=${mbDpr},user-scalable=no`;
        let docl = document.documentElement;

        docl.setAttribute("data-dpr", dpr);
        // 获取mate带viewport的元素
        let viewPostMate = document.querySelector('meta[name="viewport"]');
        if (viewPostMate) {
            console.log(content, 2);
            viewPostMate.setAttribute("content", content)
        } else {
            // 添加新的mate到header
            let newMate = document.createElement("mate");
            newMate.setAttribute("name", "viewport")
            newMate.setAttribute("content", content)
            let sd = document.head.appendChild(newMate);
            console.log("添加的元素为什么没有展示", sd);
        }

    }

    function handleRem() {
        //初始化rem
        handleRootFontSize();

        //监听布局宽高发生改变
        window.addEventListener("resize", handleRootFontSize)

        /**
         * 处理root Html的fontSize
         */
        function handleRootFontSize() {
            let clientWidth = document.documentElement.getBoundingClientRect().width ||
                window.innerWidth || document.clientWidth;
            console.log("clientWidth", clientWidth);
            if (clientWidth) {
                clientWidth = Math.min(clientWidth, MAX_WIDTH * dpr);
                clientWidth = Math.max(clientWidth, MIN_WIDTH * dpr);
            }

            console.log("maxWidth", (MAX_WIDTH * dpr));
            console.log("minWidth", (MIN_WIDTH * dpr));

            let rem = clientWidth / 18.75;
            document.documentElement.style.fontStyle = rem;
        }
    }
})();

默认的html结构

打印日志如下

HTML源代码如下