It is nearly impossible to evaluate a full-stack developer, data science candidate, or devops candidate without seeing some code. In-person interviews and other subjective forms of evaluation are inaccurate sources of bias. So, looking at actual work is critical for employers to get the right people in the door.
What do if you are a candidate
Having an actual portfolio can set developers, data science, and devops job-seekers apart from other applicants. However, candidates may not have publicly referenceable work—everything they’ve done is covered by NDA or intellectual property contract clauses. They may also be too entry-level to have any referenceable work at all.
One way for candidates to create a portfolio is to build something useful that they put on GitHub (or whatever replaces it once Microsoft screws it up the way it did Yammer) that employers can look at to set them apart from the other applicants. As a hiring manager, I fast-track people with GitHub-hosted work I can look at.
What to do if you are hiring
As an employer, after you’ve used such public work to screen candidates, you should consider creating a project for the applicants who passed the initial public-code test to complete. Such projects let you evaluate the candidates in your specific context, and it gives the candidates a better sense of the work they’ll do.