Get element by PART of class name [JavaScript]

Question

I'm trying to make a chrome extension. A part of the code (early on in the making of this extension) involves fetching several elements by their class name. There are several elements whos class name all look like this: "scollerItem [AlotOfRandomCharacters]". So I'm trying to list all classNames that start with "scrollerItem", but i'm not quite sure how to go about it.

So here's my code so far:

function initRE(){
    var matchingItems = [];
    var allElements = document.getElementsByTagName("div");
    for(i=0; i < allElements.length; i++)
    {
        if ( allElements [i].className == "scrollerItem" && "*" )
        {
            matchingItems.push(allElements[i]);
        }
    }
    alert(matchingItems[0]);
}

allElements is listed in the breakpoint watchlist as "HTMLCollection(623)" (roughly), but nothing is forwarded to the "matchingItems" array. I've tried [i].className.contains and .includes

Direct copy of one of the HTML Elements in question:

<div class="scrollerItem s1d8yj03-2 ebdCEL Post t3_agnhuk  s1ukwo15-0 RqhAo" id="t3_agnhuk" tabindex="-1">

Why not `document.getElementsByClassName('scrollerItem')`? – connexo Jan 16 '19 at 22:00 — connexo, Jan 16 '19 at 22:00

GreenTeaCake · Answer 1 · 2019-01-16T22:11:39.210

You can try to use Document.querySelectorAll() with a CSS selector matching all classes starting with your target string.

let elems = document.querySelectorAll("div[class^='scrollerItem'], div[class*=' scrollerItem]");
let classes = Array.from(elems).map(e => Array.from(e.classList)).reduce((arr, res) => {
    res = res.concat(arr);
    return res;
}, []).filter(cls => cls.startsWith('scrollerItem'))

Additional explanation of CSS selector syntax: Is there a CSS selector by class prefix?

score 3 · Answer 2 · answered Jan 16 '19 at 21:28

Since the class scrollerItem exists on the element, you can use document.querySelectorAll() with the .scrollerItem as the query:

const result = document.querySelectorAll('.scrollerItem');

console.log(Array.from(result));

<div class="scrollerItem s1d8yj03-2 ebdCEL Post t3_agnhuk  s1ukwo15-0 RqhAo" id="t3_agnhuk" tabindex="-1">

Jack Bashford · Answer 3 · 2019-01-16T22:04:40.000

1

Use classList not className:

if (allElements[i].classList.contains("scrollerItem") {...}

edited Jan 16 '19 at 22:04

answered Jan 16 '19 at 21:17

Jack Bashford

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Thanks. Had to alter it to ` if (allElements[i].classList.contains("scrollerItem")) { ` but it's working now. Problem now seems to be it prints "[object HTMLDivElement]" but im sure i'll get around that tomorrow. – svemal Jan 16 '19 at 21:33
That's because `toString()` is being called upon it. Try `alert(matchingItems[0].toSource()` to fix it. – Jack Bashford Jan 16 '19 at 21:41
`classList` is not an `Array` and has no `includes` method. Instead it has a `contains` method. – connexo Jan 16 '19 at 22:01
My bad @connexo, fixed now. – Jack Bashford Jan 16 '19 at 22:04

Get element by PART of class name [JavaScript]

3 Answers3