Why won't Playwright's setViewportSize work as expected?

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1

I’m working on an automation test suite using Playwright on Windows 10 and trying to set a specific viewport size for my browser context using the setViewportSize method. However, whenever I run my script, the browser window doesn’t adjust to the dimensions I specify. I’m using Playwright version 1.22, and I’ve tried several variations, but nothing seems to work. I expect my web application to render differently based on the viewport size, so it’s crucial for my visual tests. Has anyone else faced this issue or knows a workaround?

2

Hey there, I remember hitting the same frustration when I first started using Playwright. It’s a common hiccup when you’re getting used to the APIs.

The root of the issue often lies in the timing and scope of where setViewportSize is called. If you set it after the page is loaded, it might not apply correctly because the DOM may already be rendered at a different size. To fix this, ensure that the viewport size is set right after creating a new context and before loading your page.

Here is the snippet that worked for me:

const { chromium } = require('playwright');

(async () => {
  const browser = await chromium.launch();
  const context = await browser.newContext();
  await context.setViewportSize({ width: 1280, height: 720 });

  const page = await context.newPage();
  await page.goto('https://example.com');

  // ... your test code

  await browser.close();
})();

This code sets the viewport size immediately after creating the context, ensuring that the page loads with the correct dimensions. Make sure you watch out for any asynchronous operations that could alter the loading sequence inadvertently.

As a quick tip, always double-check your Playwright and Node.js versions, as mismatches can sometimes cause unexpected behavior. Also, reviewing the order of operations in your script can highlight where things might be out of sequence.

3

I encountered a similar blocker on a recent project and realized my approach needed some tweaking. Initially, using setViewportSize seemed straightforward, but the dimensions weren’t applying as anticipated.

Upon deeper inspection, I found that the browser’s window size constraints could interfere with the viewport settings. Adjusting the context arguments instead of relying solely on setViewportSize can provide better control over dimensions and scaling issues that arise with high DPI displays or specific OS configurations.

Here’s how you can structure your setup:

const { firefox } = require('playwright');

(async () => {
  const browser = await firefox.launch({
    headless: false,
    args: ['--window-size=1280,720']
  });

  const context = await browser.newContext();
  const page = await context.newPage();

  await page.setViewportSize({ width: 1280, height: 720 });
  await page.goto('https://example.com');

  // ... your test code

  await browser.close();
})();

Setting initial window dimensions alongside your viewport adjustments can help ensure consistent behavior. Be mindful of how different browser versions interpret argument overrides, especially across operating systems.

Another point to consider is testing in both headless and headed modes, since viewport behavior can vary between them. Keeping dependencies updated can also help avoid issues caused by outdated implementations.