How to get elements with multiple classes

Say I have this:

<div class="class1 class2"></div>

How do I select this div element?

document.getElementsByClassName('class1')[0].getElementsByClassName('class2')[0]

That does not work.

I know that, in jQuery, it is $('.class1.class2'), but I'd like to select it with vanilla JavaScript.

It's actually very similar to jQuery:

document.getElementsByClassName('class1 class2')

MDN Doc getElementsByClassName

AND (both classes)

var list = document.getElementsByClassName("class1 class2");
var list = document.querySelectorAll(".class1.class2");

OR (at least one class)

var list = document.querySelectorAll(".class1,.class2");

XOR (one class but not the other)

var list = document.querySelectorAll(".class1:not(.class2),.class2:not(.class1)");

NAND (not both classes)

var list = document.querySelectorAll(":not(.class1),:not(.class2)");

NOR (not any of the two classes)

var list = document.querySelectorAll(":not(.class1):not(.class2)");

querySelectorAll with standard class selectors also works for this.

document.querySelectorAll('.class1.class2');

As @filoxo said, you can use document.querySelectorAll.

If you know that there is only one element with the class you are looking for, or you are interested only in the first one, you can use:

document.querySelector('.class1.class2');

BTW, while .class1.class2 indicates an element with both classes, .class1 .class2 (notice the whitespace) indicates an hierarchy - and element with class class2 which is inside en element with class class1:

<div class='class1'>
  <div>
    <div class='class2'>
      :
      :

And if you want to force retrieving a direct child, use > sign (.class1 > .class2):

<div class='class1'>
  <div class='class2'>
    :
    :

For entire information about selectors:
https://www.w3schools.com/jquery/jquery_ref_selectors.asp

Okay this code does exactly what you need:

HTML:

<div class="class1">nothing happens hear.</div>

<div class="class1 class2">This element will receive yout code.</div>

<div class="class1">nothing happens hear.</div>

JS:

function getElementMultipleClasses() {
    var x = document.getElementsByClassName("class1 class2");
    x[0].innerHTML = "This is the element you want";
}
getElementMultipleClasses();

Hope it helps! ;)

html

<h2 class="example example2">A heading with class="example"</h2>

javascritp code

var element = document.querySelectorAll(".example.example2");
element.style.backgroundColor = "green";

The querySelectorAll() method returns all elements in the document that matches a specified CSS selector(s), as a static NodeList object.

The NodeList object represents a collection of nodes. The nodes can be accessed by index numbers. The index starts at 0.

also learn more about https://www.w3schools.com/jsref/met_document_queryselectorall.asp

== Thank You ==

const matches = document.querySelectorAll("div.note, div.alert");

know more

actually @bazzlebrush 's answer and @filoxo 's comment helped me a lot.

I needed to find the elements where the class could be "zA yO" OR "zA zE"

Using jquery I first select the parent of the desired elements:

(a div with class starting with 'abc' and style != 'display:none')

var tom = $('div[class^="abc"][style!="display: none;"]')[0];                   

then the desired children of that element:

var ax = tom.querySelectorAll('.zA.yO, .zA.zE');

works perfectly! note you don't have to do document.querySelector you can as above pass in a pre-selected object.