【rem】自定义rem.js

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/qq_35448976/article/details/82796832

console.time("test");
!function(win, option) {
    var count = 0,
        designWidth = option.designWidth,
        designHeight = option.designHeight || 0,
        designFontSize = option.designFontSize || 20,
        callback = option.callback || null,
        root = document.documentElement,
        body = document.body,
        rootWidth, newSize, t, self;
    root.style.width = '100%';
    //返回root元素字体计算结果
    function _getNewFontSize() {
        var scale = designHeight !== 0 ? Math.min(win.innerWidth / designWidth, win.innerWidth / designWidth) : win.innerWidth / designWidth;
        return parseInt( scale * 10000 * designFontSize ) / 10000;
    }
    !function () {
        rootWidth = root.getBoundingClientRect().width;
        self = self ? self : arguments.callee;
        //如果此时屏幕宽度不准确，就尝试再次获取分辨率，只尝试20次，否则使用win.innerWidth计算
        if( rootWidth !== win.innerWidth &&  count < 20 ) {
            win.setTimeout(function () {
                count++;
                self();
            }, 0);
        } else {
            newSize = _getNewFontSize();
            //如果css已经兼容当前分辨率就不管了
            if( newSize + 'px' !== getComputedStyle(root)['font-size'] ) {
                root.style.fontSize = newSize + "px";
                return callback && callback(newSize);
            };
        };
    }();
    //横竖屏切换的时候改变fontSize，根据需要选择使用
    win.addEventListener("onorientationchange" in window ? "orientationchange" : "resize", function() {
        clearTimeout(t);
        t = setTimeout(function () {
            self();
        }, 300);
    }, false);
}(window, {
    designWidth: 375,
    designHeight: 640,
    designFontSize: 10,
    callback: function (argument) {
        console.timeEnd("test")
    }
});