javascript - 以 em 为单位获取用户视口(viewport)大小

Question

编辑
以下代码获取 em 的大小，但与我的 css 不对应。

function doOnOrientationChange() {
        // Orientation of device has changed, change the size of map and move the maphelp (if required)
        var eminpx = $("#1em").width();
        var largescreeninpx = eminpx*66.236;
        switch(window.orientation) {
            case -90:
            case 90:
                // Orientation is landscape
                console.log('66.236ems in px: ' + largescreeninpx + '. Screen width: ' + screen.height);
                $("#map").height(screen.width*0.7); // The screen width is the viewport height of the device because we're in landscape orientation
                // Will only work if we can actually get the em value of the width
                if (screen.height < largescreeninpx) {
                     // Small or medium screen, show map help below map
                     console.log('small screen');
                    $("#maphelp").css('margin-top', 0);
                } else {
                    // Larger screen, show map and map help side-by-side
                    $("#maphelp").css('margin-top', -screen.width*0.7);
                }
                break; 
            default:
                // Orientation is portrait
                alert('66.23ems in px: ' + largescreeninpx + '. Screen width: ' + screen.width);
                $("#map").height(screen.height*0.7);
                // Will only work if we can actually get the em value of the width
                if (screen.width < largescreeninpx) {
                     // Small or medium screen, show map help below map
                    $("#maphelp").css('margin-top', 0);
                } else {
                    // Larger screen, show map and map help side-by-side
                    $("#maphelp").css('margin-top', -screen.height*0.7);
                }
                break;
        }
    }

尽管在 CSS 中横向 iPad 不会触发 @media screen and (min-width: 30em) and (max-width: 63.236em) {...}(意味着它有一个宽度超过63.236ems)，在JS中触发console.log('small screen')，通过JS获取时显示屏幕宽度小于66.236ems？

原始问题(几乎已回答) 我正在尝试围绕“The Goldilocks Approach”创建一个网站。电子表格中的一切都很好，但我正在尝试动态设置嵌入式 map 的高度，以便它始终是用户当前视口(viewport)高度的 90%。然而， map 旁边也可以是一些“ map 帮助”，允许浏览器视口(viewport)足够大(在本例中为 66.23ems。纵向的 iPad 超过 66.23ems)。下面是我的代码，它被注释以显示不起作用的内容。

function doOnOrientationChange() {
        // Orientation of device has changed, change the size of map and move the maphelp (if required)
        switch(window.orientation) {
            case -90:
            case 90:
                // Orientation is landscape
                $("#map").height(screen.width*0.9); // The screen width is the viewport height of the device because we're in landscape orientation
                if ($(window).width() > 66.23) { // Need this in ems
                     // Small or medium screen, show map help below map
                    $("#maphelp").css('margin-top', 0);
                } else {
                    // Larger screen, show map and map help side-by-side
                    $("#maphelp").css('margin-top', -screen.width*0.9);
                }
                break; 
            default:
                // Orientation is portrait
                if ($(window).width() < 66.23) { // Need this in ems
                     // Small or medium screen, show map help below map
                    $("#maphelp").css('margin-top', 0);
                } else {
                    // Larger screen, show map and map help side-by-side
                    $("#maphelp").css('margin-top', -screen.height*0.9);
                }
                break;
        }
    }

所以，我的问题是，我怎样才能通过 checkin ems 让它触发正确的响应？

Answer 1

创建一个跨度如下:

<span id="one_em">M</span>

像这样的 CSS:

#one_em {
    display:none;
    width: 1em;
}

然后使用jquery获取#one_em元素的宽度。

const emWidth = $("#one_em").width();

注意:使用 1em 作为 id 会导致某些浏览器无法正确连接 CSS，因为有效的 HTML 4 id 必须以字母开头。使用 M 所以宽度实际上是 1 M 宽。