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August 16, 2011 08:21
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A better way to detect :before and :after CSS pseudo-element selector support using JavaScript (Modernizr takes similar route)
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body { | |
font: normal small Helvetica, Arial, Verdana, sans-serif; | |
} | |
h1 { | |
border-bottom: 1px solid #C00; | |
color: #666; | |
font-weight: bold; | |
margin-bottom: 10px; | |
} | |
div { | |
border: 1px dashed #333; | |
padding: 10px; | |
} | |
div, | |
div p { | |
margin-bottom: 10px; | |
} | |
code { | |
color: blue; | |
} | |
ul { | |
list-style: disc; | |
margin-left: 10px; | |
padding-left: 10px; | |
} | |
.before #apply:before { | |
color: red; | |
content: "before"; | |
display: inline-block; | |
margin: 0 5px 5px 0; | |
} | |
.after #apply:after { | |
color: green; | |
content: "after"; | |
display: inline-block; | |
margin: 0 0 0 55px; | |
} |
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<h1>Detection script for CSS :before and :after support</h1> | |
<div> | |
<p>This script detects support of the CSS selectors <code>:before</code> and <code>:after</code> by:</p> | |
<ul> | |
<li>Adding two empty paragraph elements to the page (effectively their height each is zero).</li> | |
<li>Adding a style element to the page (+inserting the relevant <code>:before</code>/<code>:after</code> code).</li> | |
<li>Checking the height of the element using offsetHeight.</li> | |
<li>If the height is greater or equal to 1 then we know the content was added so support is detected.</li> | |
<li>Much like <a href="http://www.modernizr.com/">Modernizr</a> we add relevant class names to the main <code>html</code> element</li> | |
</ul> | |
</div> | |
<p id="apply">Paragraph 1</p> | |
<p>Paragraph 2</p> |
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window.onload = function() { | |
var doc = document, | |
html = doc.documentElement, | |
body = doc.body, | |
paraBefore = doc.createElement('p'), | |
paraAfter = doc.createElement('p'), | |
styleBefore = doc.createElement('style'), | |
styleAfter = doc.createElement('style'), | |
heightBefore, | |
heightAfter, | |
selectorsBefore = '#testbefore:before { content: "before"; }', | |
selectorsAfter = '#testafter:after { content: "after"; }'; | |
// Internet Explorer seems to need a type attribute to recognise a stylesheet? | |
styleBefore.type = 'text\/css'; | |
styleAfter.type = 'text\/css'; | |
paraBefore.id = 'testbefore'; | |
paraAfter.id = 'testafter'; | |
// For Internet Explorer... | |
if (styleBefore.styleSheet) { | |
styleBefore.styleSheet.cssText = selectorsBefore; | |
styleAfter.styleSheet.cssText = selectorsAfter; | |
} else { | |
styleBefore.appendChild(doc.createTextNode(selectorsBefore)); | |
styleAfter.appendChild(doc.createTextNode(selectorsAfter)); | |
} | |
body.appendChild(styleBefore); | |
body.appendChild(styleAfter); | |
body.appendChild(paraBefore); | |
body.appendChild(paraAfter); | |
heightBefore = doc.getElementById('testbefore').offsetHeight; | |
heightAfter = doc.getElementById('testafter').offsetHeight; | |
console.log(heightBefore, heightAfter); | |
if (heightBefore >= 1) { | |
html.className += ' before'; | |
body.removeChild(styleBefore); | |
body.removeChild(paraBefore); | |
} | |
if (heightAfter >= 1) { | |
html.className += ' after'; | |
body.removeChild(styleAfter); | |
body.removeChild(paraAfter); | |
} | |
}; |
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