Here are two ways to deal with this.
I don’t know if the following will exactly match your needs. It’s a simple enough solution to the problem, but at least it doesn’t use RegEx to manipulate HTML tags. It performs pattern matching against the raw text and then uses the DOM to manipulate the content.
First approach
This approach creates only one <span> tag per match, leveraging some less common browser APIs.
(See the main problem of this approach below the demo, and if not sure, use the second approach).
The Range class represents a text fragment. It has a surroundContents function that lets you wrap a range in an element. Except it has a caveat:
This method is nearly equivalent to
newNode.appendChild(range.extractContents()); range.insertNode(newNode). After surrounding, the boundary points of the range includenewNode.An exception will be thrown, however, if the
Rangesplits a non-Textnode with only one of its boundary points. That is, unlike the alternative above, if there are partially selected nodes, they will not be cloned and instead the operation will fail.
Well, the workaround is provided in the MDN, so all’s good.
So here’s an algorithm:
- Make a list of
Textnodes and keep their start indices in the text - Concatenate these nodes’ values to get the
text -
Find matches over the text, and for each match:
- Find the start and end nodes of the match, comparing the the nodes’ start indices to the match position
- Create a
Rangeover the match - Let the browser do the dirty work using the trick above
- Rebuild the node list since the last action changed the DOM
Here’s my implementation with a demo:
function highlight(element, regex) {
var document = element.ownerDocument;
var getNodes = function() {
var nodes = [],
offset = 0,
node,
nodeIterator = document.createNodeIterator(element, NodeFilter.SHOW_TEXT, null, false);
while (node = nodeIterator.nextNode()) {
nodes.push({
textNode: node,
start: offset,
length: node.nodeValue.length
});
offset += node.nodeValue.length
}
return nodes;
}
var nodes = getNodes(nodes);
if (!nodes.length)
return;
var text = "";
for (var i = 0; i < nodes.length; ++i)
text += nodes[i].textNode.nodeValue;
var match;
while (match = regex.exec(text)) {
// Prevent empty matches causing infinite loops
if (!match[0].length)
{
regex.lastIndex++;
continue;
}
// Find the start and end text node
var startNode = null, endNode = null;
for (i = 0; i < nodes.length; ++i) {
var node = nodes[i];
if (node.start + node.length <= match.index)
continue;
if (!startNode)
startNode = node;
if (node.start + node.length >= match.index + match[0].length)
{
endNode = node;
break;
}
}
var range = document.createRange();
range.setStart(startNode.textNode, match.index - startNode.start);
range.setEnd(endNode.textNode, match.index + match[0].length - endNode.start);
var spanNode = document.createElement("span");
spanNode.className = "highlight";
spanNode.appendChild(range.extractContents());
range.insertNode(spanNode);
nodes = getNodes();
}
}
// Test code
var testDiv = document.getElementById("test-cases");
var originalHtml = testDiv.innerHTML;
function test() {
testDiv.innerHTML = originalHtml;
try {
var regex = new RegExp(document.getElementById("regex").value, "g");
highlight(testDiv, regex);
}
catch(e) {
testDiv.innerText = e;
}
}
document.getElementById("runBtn").onclick = test;
test();.highlight {
background-color: yellow;
border: 1px solid orange;
border-radius: 5px;
}
.section {
border: 1px solid gray;
padding: 10px;
margin: 10px;
}<form class="section">
RegEx: <input id="regex" type="text" value="[A-Z].*?\." /> <button id="runBtn">Highlight</button>
</form>
<div id="test-cases" class="section">
<div>foo bar baz</div>
<p>
<b>HTML</b> is a language used to make <b>websites.</b>
It was developed by <i>CERN</i> employees in the early 90s.
<p>
<p>
This program is <a href="https://stackoverflow.com/questions/31275446/beta.html">not stable yet. Do not use this in production yet.</a>
</p>
<div>foo bar baz</div>
</div>Ok, that was the lazy approach which, unfortunately doesn’t work for some cases. It works well if you only highlight across inline elements, but breaks when there are block elements along the way because of the following property of the extractContents function:
Partially selected nodes are cloned to include the parent tags necessary to make the document fragment valid.
That’s bad. It’ll just duplicate block-level nodes. Try the previous demo with the baz\s+HTML regex if you want to see how it breaks.
Second approach
This approach iterates over the matching nodes, creating <span> tags along the way.
The overall algorithm is straightforward as it just wraps each matching node in its own <span>. But this means we have to deal with partially matching text nodes, which requires some more effort.
If a text node matches partially, it’s split with the splitText function:
After the split, the current node contains all the content up to the specified offset point, and a newly created node of the same type contains the remaining text. The newly created node is returned to the caller.
function highlight(element, regex) {
var document = element.ownerDocument;
var nodes = [],
text = "",
node,
nodeIterator = document.createNodeIterator(element, NodeFilter.SHOW_TEXT, null, false);
while (node = nodeIterator.nextNode()) {
nodes.push({
textNode: node,
start: text.length
});
text += node.nodeValue
}
if (!nodes.length)
return;
var match;
while (match = regex.exec(text)) {
var matchLength = match[0].length;
// Prevent empty matches causing infinite loops
if (!matchLength)
{
regex.lastIndex++;
continue;
}
for (var i = 0; i < nodes.length; ++i) {
node = nodes[i];
var nodeLength = node.textNode.nodeValue.length;
// Skip nodes before the match
if (node.start + nodeLength <= match.index)
continue;
// Break after the match
if (node.start >= match.index + matchLength)
break;
// Split the start node if required
if (node.start < match.index) {
nodes.splice(i + 1, 0, {
textNode: node.textNode.splitText(match.index - node.start),
start: match.index
});
continue;
}
// Split the end node if required
if (node.start + nodeLength > match.index + matchLength) {
nodes.splice(i + 1, 0, {
textNode: node.textNode.splitText(match.index + matchLength - node.start),
start: match.index + matchLength
});
}
// Highlight the current node
var spanNode = document.createElement("span");
spanNode.className = "highlight";
node.textNode.parentNode.replaceChild(spanNode, node.textNode);
spanNode.appendChild(node.textNode);
}
}
}
// Test code
var testDiv = document.getElementById("test-cases");
var originalHtml = testDiv.innerHTML;
function test() {
testDiv.innerHTML = originalHtml;
try {
var regex = new RegExp(document.getElementById("regex").value, "g");
highlight(testDiv, regex);
}
catch(e) {
testDiv.innerText = e;
}
}
document.getElementById("runBtn").onclick = test;
test();.highlight {
background-color: yellow;
}
.section {
border: 1px solid gray;
padding: 10px;
margin: 10px;
}<form class="section">
RegEx: <input id="regex" type="text" value="[A-Z].*?\." /> <button id="runBtn">Highlight</button>
</form>
<div id="test-cases" class="section">
<div>foo bar baz</div>
<p>
<b>HTML</b> is a language used to make <b>websites.</b>
It was developed by <i>CERN</i> employees in the early 90s.
<p>
<p>
This program is <a href="https://stackoverflow.com/questions/31275446/beta.html">not stable yet. Do not use this in production yet.</a>
</p>
<div>foo bar baz</div>
</div>This should be good enough for most cases I hope. If you need to minimize the number of <span> tags it can be done by extending this function, but I wanted to keep it simple for now.