Lazy loading is one of the most effective techniques for improving frontend application performance. When applied incorrectly, however, it can negatively impact user experience and introduce hard-to-detect bugs.
In this article, we explain when lazy loading makes sense and when it’s better to avoid it.
What Is Lazy Loading?
Lazy loading is the practice of deferring the loading of resources that are not required during the initial page render.
What Should Be Lazy Loaded?
- images outside the initial viewport,
- rarely used components,
- heavy libraries,
- sections available after user interaction.
What Should Not Be Lazy Loaded?
- critical application logic,
- elements visible immediately on page load,
- key fonts,
- primary navigation.
Lazy Loading and SEO
Modern search engines handle lazy loading well, but:
- content must be present in the DOM,
- JavaScript must not block rendering,
- progressive enhancement should be applied.
Common Mistakes
- excessive lazy loading,
- missing fallbacks,
- accessibility (a11y) issues.
Summary
Lazy loading is an optimization tool, not a default strategy. Used consciously, it delivers real benefits for both performance and user experience.