In plain JavaScript you would use something like:
// Single
document.querySelector(".onediv").classList.add("red");
// Multiple (deeply nested)
document.querySelectorAll(".onediv:first-child").forEach(EL => EL.classList.add("red"));
Or by Parent Element using Element.firstElementChild:
// Single Parent
document.querySelector(".alldivs").firstElementChild.classList.add("red");
// Multiple parents
document.querySelector(".alldivs").forEach(EL => EL.firstElementChild.classList.add("red"));
jQuery get first child
Use: $(".onediv").eq(0)
Other examples of selectors and methods targeting the first LI inside an UL:
| Syntax | Type | Example |
|---|---|---|
| .eq() | Method | $("li").eq(0) |
| .first() | Method | $("li").first() |
| :eq() | Selector | $("li:eq(0)") |
| :first | Selector | $("li:first") |
| :first-child | Selector | $("li:first-child") |
| :lt() | Selector | $("li:lt(1)") |
| :nth-child() | Selector | $("li:nth-child(1)") |
| .slice() | Method | $("li").slice(0,1) |
There are some slight differences in how they operate regarding depth. Play with the below demo examples:
$("select").on("change", function() {
$("li").removeClass("red");
new Function(`return (${this.value})`)();
}).trigger("change");.red {color: red;}
option[disabled] {font-size: 1.4em; color: blue;}<select>
<option disabled>jQuery examples:</option>
<option>$("li").eq(0).addClass("red")</option>
<option>$("li:eq(0)").addClass("red")</option>
<option>$("li").first().addClass("red")</option>
<option>$("li:first").addClass("red")</option>
<option>$("li:first-child").addClass("red")</option>
<option>$("li:lt(1)").addClass("red")</option>
<option>$("li:nth-child(1)").addClass("red")</option>
<option>$("li").slice(0,1).addClass("red")</option>
<option disabled>JavaScript examples:</option>
<option>document.querySelector("li").classList.add("red")</option>
<option>document.querySelectorAll("li:first-child").forEach(EL => EL.classList.add("red"))</option>
<option disabled>Mixed jQuery + JavaScript</option>
<option>$("li")[0].classList.add("red")</option>
</select>
<ul>
<li>1</li>
<li>2
<ul>
<li>2.1</li>
<li>2.2</li>
</ul>
</li>
<li>3</li>
</ul>
<script src="https://code.jquery.com/jquery-3.6.0.js"></script>you can also use [i] to get the JS Element by index out of the jQuery elements collection like eg:
$("li")[0]
but now that you have the native JS Element representation you have to use JavaScript methods eg:
$("li")[0].classList.add("active"); // Adds class "active" to the first LI in the DOM
or you can (don’t – it’s bad design) wrap it back into a jQuery object
$( $("li")[0] ).addClass("active"); // Don't! Use .eq() instead