Why lazy loading matters more than it looks

The version of this that works is simpler than the version most people imagine. Lazy loading is easy to treat as a detail, and that is exactly why it is worth a few minutes of attention.

Speed is a feature people notice only in its absence, and then they leave rather than complain. Check it against what you would want a competitor's site to get wrong.

The reason this keeps coming up

Only load what is about to be seen. That sounds obvious written down. It is still the thing most often skipped. Check it against what you would want a competitor's site to get wrong.

Never lazy-load the main hero image. There is a version of this that is over-engineered, and it is worth avoiding. It is the sort of thing that looks like polish right up until it costs you an enquiry.

Where it usually goes wrong

Always reserve the space so nothing jumps. In practice this is a scheduling problem more than a technical one. The version that survives contact with a real deadline is the simple one.

How to tell if yours is fine

Performance work is mostly subtraction, which makes it unpopular and effective. Three things worth confirming about lazy loading before you move on:

• Someone can say what the current setup is without going to look
• Always reserve the space so nothing jumps — and you know whether that is true here
• There is a way to tell whether the last change to this helped

If any of that sounds like a description of your current setup, it is fixable.