计算方法，精度损失来自于浏览器将rem转成px的过程。
element.currentStyle ? element.currentStyle : window.getComputedStyle(element, null)
可以获取px小数点后的数值
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0, user-scalable=no" />
<meta name="apple-mobile-web-app-capable" content="yes">
<meta name="apple-mobile-web-app-status-bar-style" content="black">
<title></title>
<style type="text/css">
.c {
width: 1.345rem;
}
</style>
</head>
<body>
<div class="c">
</div>
<script type="text/javascript">
function getElementStyle(selector) {
var element = document.querySelector(selector);
return element.currentStyle ? element.currentStyle : window.getComputedStyle(element, null);
}
function getElementStyleValue(selector, cssAttr, isRem) {
var fontSize = parseFloat(getElementStyle(‘html‘).fontSize),
elementStyle = getElementStyle(selector);
value = parseFloat(elementStyle[cssAttr]),
isRem != false?isRem = true:‘‘;
if(isRem) {
value = (value/fontSize).toFixed(4) + "rem";
} else {
value = value.toFixed(4)+"px";
}
console.log(value);
return value;
}
var value1 = getElementStyleValue(‘.c‘, ‘width‘);
var value2 = getElementStyleValue(‘.c‘, ‘width‘, false);
console.log(value1,value2);
</script>
</body>
</html>