<!DOCTYPE html>
<style>
.red { color: red; }
</style>
<script>
document.onreadystatechange = function() {
if (document.readyState == "complete") {
var arr = ["s2","s3"];
arr.forEach(function(n) {
document.getElementById(n).className = "red";
});
}
};
</script>
<div>
<span id="s1">test</span><br />
<span id="s2">test</span><br />
<span id="s3">test</span><br />
<span id="s4">test</span><br />
</div>