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Table of Contents
1. The return value type is different
2. Comparison of selector capabilities
3. How to get multiple elements
4. Performance differences (not much impact in actual use)
5. Use suggestions
Summarize
Home Web Front-end JS Tutorial JavaScript querySelector vs getElementsByClassName

JavaScript querySelector vs getElementsByClassName

Jul 30, 2025 am 05:03 AM
DOM operation

querySelector 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.

JavaScript querySelector vs getElementsByClassName

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.

JavaScript querySelector vs getElementsByClassName

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.

    JavaScript querySelector vs getElementsByClassName
     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.

JavaScript querySelector vs getElementsByClassName

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, use querySelectorAll :

     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 and querySelectorAll , which has clearer code and better scalability.

Basically all is it, not complicated but it is easy to ignore details.

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