Chart.js responsive property and container dimension synchronization

Answer to the question

When responsive:true is set, Chart.js reads the clientWidth and clientHeight of the canvas’s parent immediately after construction. If those values are zero, the library:

• Sets the canvas width/height to 0 and skips the initial draw.
• Schedules an asynchronous check via requestAnimationFrame (or a ResizeObserver if available).
• When the observer reports a non‑zero size, the canvas is resized and the chart is rendered.

Thus the chart is deferred until the layout settles, but it does not crash or throw errors.

Preventing recursive resize events in flex‑based layouts

1. Disable the built‑in observer and resize manually

   const ctx = document.getElementById('myChart').getContext('2d');
   const chart = new Chart(ctx, {
     type: 'bar',
     data: {...},
     options: {
       responsive: false, // no automatic resize
       maintainAspectRatio: false
     }
   });
   // After layout changes
   function onContainerResize() {
     chart.resize();
   }
   

2. Throttle the observer callbacks

   const observer = new ResizeObserver(entries => {
     clearTimeout(window._resizeTimer);
     window._resizeTimer = setTimeout(() => chart.resize(), 100);
   });
   observer.observe(document.querySelector('.chart-container'));
   

Additional knobs that help:

• maintainAspectRatio:false lets the chart expand to the container’s height without recalculating the aspect ratio, reducing unnecessary resize events.
• Setting animation.duration: 0 removes the internal animation loop that can repeatedly trigger size checks when the container is unstable.

Practical checklist

• Give the flex container a min-height or explicit height so the initial measurements aren’t zero.
• Use responsive:false if you prefer full manual control.
• If you keep responsive:true, set maintainAspectRatio:false and optionally debounce resize callbacks.
• Verify the chart renders after the first non‑zero measurement by inspecting chart.width and chart.height in the console.

Diagnostic question

Do you apply any CSS that sets the flex container’s height to auto or 0 before the chart is instantiated? That rule can cause the initial zero‑size situation described above.