REM手机屏幕适配

rem
的官方定义『The font size of the root element.』，即以根节点的字体大小作为基准值进行长度计算。

head 中我们设置了：<meta name="viewport" content="width=device-width, initial-scale=1.0, minimum-scale=1.0, maximum-scale=1.0"
/>

以设计稿的宽度为640px，即：designWidth
= 640，同时设定在640px屏宽下 1rem=100px ，即：rem2px = 100。

以下具体方案共享：

链接：http://mp.weixin.qq.com/s/DpLXJhfCHsgrbgbuk25Ekw

方案1

@media
screen and (min-width: 320px) {html{font-size:50px;}}

@media
screen and (min-width: 360px) {html{font-size:56.25px;}}

@media
screen and (min-width: 375px) {html{font-size:58.59375px;}}

@media
screen and (min-width: 400px) {html{font-size:62.5px;}}

@media
screen and (min-width: 414px) {html{font-size:64.6875px;}}

@media
screen and (min-width: 440px) {html{font-size:68.75px;}}

@media
screen and (min-width: 480px) {html{font-size:75px;}}

@media
screen and (min-width: 520px) {html{font-size:81.25px;}}

@media
screen and (min-width: 560px) {html{font-size:87.5px;}}

@media
screen and (min-width: 600px) {html{font-size:93.75px;}}

@media
screen and (min-width: 640px) {html{font-size:100px;}}

@media
screen and (min-width: 680px) {html{font-size:106.25px;}}

@media
screen and (min-width: 720px) {html{font-size:112.5px;}}

@media
screen and (min-width: 760px) {html{font-size:118.75px;}}

@media
screen and (min-width: 800px) {html{font-size:125px;}}

@media
screen and (min-width: 960px) {html{font-size:150px;}}

方案2

@media
screen and (min-width: 320px) {html{font-size:312.5%;}}

@media
screen and (min-width: 360px) {html{font-size:351.5625%;}}

@media
screen and (min-width: 375px) {html{font-size:366.211%;}}

@media
screen and (min-width: 400px) {html{font-size:390.625%;}}

@media
screen and (min-width: 414px) {html{font-size:404.2969%;}}

@media
screen and (min-width: 440px) {html{font-size:429.6875%;}}

@media
screen and (min-width: 480px) {html{font-size:468.75%;}}

@media
screen and (min-width: 520px) {html{font-size:507.8125%;}}

@media
screen and (min-width: 560px) {html{font-size:546.875%;}}

@media
screen and (min-width: 600px) {html{font-size:585.9375%;}}

@media
screen and (min-width: 640px) {html{font-size:625%;}}

@media
screen and (min-width: 680px) {html{font-size:664.0625%;}}

@media
screen and (min-width: 720px) {html{font-size:703.125%;}}

@media
screen and (min-width: 760px) {html{font-size:742.1875%;}}

@media
screen and (min-width: 800px) {html{font-size:781.25%;}}

@media
screen and (min-width: 960px) {html{font-size:937.5%;}}

方案3

var designWidth = 640, rem2px = 100;

document.documentElement.style.fontSize =

((window.innerWidth / designWidth) * rem2px) + 'px';

方案4

var designWidth = 640, rem2px = 100;

document.documentElement.style.fontSize =

((((window.innerWidth / designWidth) * rem2px) / 16) * 100) + '%';、

方案4.1

var designWidth = 640, rem2px = 100;

var h = document.getElementsByTagName('html')[0];

var htmlFontSize = parseFloat(window.getComputedStyle(h, null)

.getPropertyValue('font-size'));

document.documentElement.style.fontSize =

window.innerWidth / designWidth * rem2px / htmlFontSize * 100 + '%';

方案4.2

var designWidth = 640, rem2px = 100;

var d = window.document.createElement('div');

d.style.width = '1rem';

d.style.display = "none";

var head = window.document.getElementsByTagName('head')[0];

head.appendChild(d);

var defaultFontSize = parseFloat(window.getComputedStyle(d, null).getPropertyValue('width'));

d.remove();

document.documentElement.style.fontSize =

window.innerWidth / designWidth * rem2px / defaultFontSize * 100 + '%';

最终手机端的解决方案为：

function adapt(designWidth, rem2px){

var d = window.document.createElement('div');

d.style.width = '1rem';

d.style.display = "none";

var head = window.document.getElementsByTagName('head')[0];

head.appendChild(d);

var defaultFontSize = parseFloat(window.getComputedStyle(d, null).getPropertyValue('width'));

d.remove();

document.documentElement.style.fontSize = window.innerWidth / designWidth * rem2px / defaultFontSize * 100 + '%';

var st = document.createElement('style');

var portrait = "@media
screen and (min-width: "+window.innerWidth+"px)
{html{font-size:"+((window.innerWidth/(designWidth/rem2px)/defaultFontSize)*100) +"%;}}";

var landscape = "@media
screen and (min-width: "+window.innerHeight+"px)
{html{font-size:"+((window.innerHeight/(designWidth/rem2px)/defaultFontSize)*100) +"%;}}"

st.innerHTML = portrait + landscape;

head.appendChild(st);

return defaultFontSize

};

var defaultFontSize = adapt(640, 100);

以设计稿的宽度为640px，即：designWidth = 640，同时设定在640px屏宽下 1rem=100px ，即：rem2px = 100。