JavaScript Resize_observer Guide
ResizeObserver reports element size changes for responsive components and adaptive layouts. The guide walks through Observing Size. `new ResizeObserver(entries=>{for(const e of entries){e.contentRect}})`. entry.contentRect: x,y,width,height. Observe: `observer.observe(el)`. Use for: responsive charts, text truncation detection, container-based layouts, canvas redrawing on resize. The guide is organized into 1 sections that build on each other, each pairing a prose explanation with runnable code. Related guides: Arrays, Strings, Numbers, Math, Date. This is one of 145 JavaScript guides on JS Reference — see the full list on the guides page. Practice what you learn in the JavaScript playground, and look up any unfamiliar term in the JavaScript glossary.