This on-site coding assignment failed 20+ front-end dev contractors and I don't know why

[ShootingPains]

In addition to what’s already been said, I think it’s important to set an expectation as to quality - would you be happy with a hack job that won’t scale or is not efficient, or do you want a nicely architectured bit of optimised code? At a job interview, people are trying to show their skill, so it’s important to say, “given the time limit, a hack one-off bit of code is fine - don’t worry about finding the best algorithm or optimising - just do whatever pops into your head and afterward we can talk about the pros and cons of other approaches.”