JavaScript querySelector vs getElementsByClassName
Jul 30, 2025 am 05:03 AMquerySelector returns a static single element or NodeList, getElementsByClassName returns a dynamic HTMLCollection; 2. querySelector supports complex CSS selectors, the latter only supports class names; 3. QuerySelectorAll should be used when obtaining multiple elements; 4. The performance difference is extremely small, modern development recommends the use of querySelector and querySelectorAll first, because it is more flexible and has stronger code readability, and getElementsByClassName is used unless real-time collection is required.
In JavaScript, querySelector
and getElementsByClassName
are both methods used to obtain page elements, but they are obviously different in terms of usage, return value type, and performance. Which one to choose depends on your specific needs.

1. The return value type is different
This is the most core difference between the two.
-
getElementsByClassName
Returns a real-time HTMLCollection (class array object).
Meaning: If you modify the DOM in the future, this collection will be automatically updated.const elements = document.getElementsByClassName('my-class'); console.log(elements); // Real-time collection, dynamic update
querySelector
Returns a static NodeList or a single element (the first match).
Even if the DOM changes subsequently, the obtained results will not be updated.const element = document.querySelector('.my-class'); console.log(element); // Return only the first matching element
? Tips:
querySelectorAll
returns NodeList,querySelector
returns a single element.
2. Comparison of selector capabilities
getElementsByClassName
It can only be searched by class names, and the function is single.document.getElementsByClassName('active');
querySelector
Supports full CSS selectors for more flexibility.document.querySelector('.header .nav li.active'); document.querySelector('div[data-type="user"]'); document.querySelector('input[name="email"]');
? If you need complex choices (such as properties, nesting, pseudo-classes, etc.),
querySelector
is the only choice.
3. How to get multiple elements
getElementsByClassName
is born to return all matching elements (HTMLCollection).querySelector
returns only the first match.If you want to use
querySelector
to get multiple elements, usequerySelectorAll
:const elements = document.querySelectorAll('.my-class');
Note:
querySelectorAll
returns a static NodeList and will not be automatically updated with DOM changes.
4. Performance differences (not much impact in actual use)
-
getElementsByClassName
may trigger reflow when frequently accessed, and its performance is slightly higher in theory, but modern browsers are very optimized. -
querySelector
/querySelectorAll
parses CSS selectors, slightly slower, but in most scenarios, the difference can be ignored.
? Don't sacrifice readability and flexibility for performance. Unless you operate thousands of elements in a high frequency loop, you don't have to worry about this performance difference.
5. Use suggestions
Scene | Recommended method |
---|---|
Just want to get the first element matching the class name | document.querySelector('.className')
|
Get all elements matching class names | document.querySelectorAll('.className')
|
Collections that require real-time updates (rare) | document.getElementsByClassName('className')
|
Use complex selectors (properties, nesting, etc.) | querySelector / querySelectorAll
|
Compatibility requirements for extremely old browsers | Both support IE8, but querySelector has some restrictions in IE8 |
Summarize
-
getElementsByClassName
is simple, fast, and returns dynamic collections, but has limited functionality. -
querySelector
is more powerful and flexible, supports all CSS selectors, and is the first choice for modern development. - In most cases, it is recommended to use
querySelector
andquerySelectorAll
, which has clearer code and better scalability.
Basically all is it, not complicated but it is easy to ignore details.
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