By the time Yarn appeared, JavaScript dependency management had already become part of ordinary web development. Even a website that rendered through WordPress or another CMS could still have a front-end build process with packages for Sass, bundling, linting and browser support. The project might not be a JavaScript application, but it still depended on the JavaScript ecosystem to build properly.
That made package installation more important than it first appeared. If one developer installed a slightly different dependency tree from another developer, or if a deployment environment resolved packages differently from a local machine, the project could behave inconsistently. Those problems are frustrating because they do not always look like dependency issues at first. They look like strange build failures, different output or a project that only works on one machine.
Why Repeatable Installs Matter
A build process should be boring. If I run the install command today and another developer runs it tomorrow, we should end up with the same working project unless something has intentionally changed. That sounds obvious, but dependency ranges and nested packages can make it less certain than it should be.
The attraction of Yarn was that it treated repeatability as a central problem. Lockfiles, faster installs and more predictable behaviour made sense because front-end tooling had become infrastructure. A website could depend on the build output, and the build output depended on the packages being installed correctly.
The Agency Problem
In agency work, projects are often revisited after weeks or months. A developer might return to a site to make a small change and discover that the build process no longer works cleanly. Maybe a dependency has changed. Maybe the original install was never documented. Maybe the project only works on the machine that first built it. That is not a good place to be.
This is why dependency management is not just a developer preference. It affects maintenance. If the process for rebuilding assets is unreliable, a simple content or design change can become unnecessarily risky. A tool that makes installs more predictable gives the project a better chance of surviving normal agency handovers.
Yarn Was Not A Magic Fix
Yarn did not remove the need to understand the dependency tree. A project could still have too many packages, unmaintained packages or scripts nobody understood. Faster and more reliable installs are useful, but they do not replace good judgement about what the project should depend on in the first place.
That is the part I would keep coming back to. Every package added to a project becomes something the project has to trust. Some are clearly worth it. Others get added because they solve a small problem quickly and then remain in the project for years. A better package manager helps, but it does not decide which dependencies are justified.
Retrospective Thoughts
Retrospectively, Yarn felt important because it made a hidden part of development more visible. Installing dependencies is not the exciting part of a project, but it affects every person who has to build, test or deploy the code. If that step is unreliable, the whole workflow feels weaker.
For me, the lesson was simple. If a website or application depends on a JavaScript build process, the install process needs to be repeatable and documented. Yarn was one answer to that problem in 2016, but the wider point is that tooling should be treated as part of the project, not as something that only exists on one developer’s machine.