You can use the jquery highlight effect.
But if you are interested in raw javascript code, take a look at what I got
Simply copy paste into an HTML, open the file and click "highlight" - this should highlight the word "fox". Performance wise I think this would do for small text and a single repetition (like you specified)
function highlight(text) {
var inputText = document.getElementById("inputText");
var innerHTML = inputText.innerHTML;
var index = innerHTML.indexOf(text);
if (index >= 0) {
innerHTML = innerHTML.substring(0,index) + "<span class='highlight'>" + innerHTML.substring(index,index+text.length) + "</span>" + innerHTML.substring(index + text.length);
inputText.innerHTML = innerHTML;
}
}
.highlight {
background-color: yellow;
}
<button onclick="highlight('fox')">Highlight</button>
<div id="inputText">
The fox went over the fence
</div>
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