The bill will be passed, then the state department of labor will issue rules regarding its enforcement. That's how government works.
When Colorado did the same thing, the Colorado department of labor issued rules that required employers to use a "good-faith and reasonable* estimate" of the salary range. You can expect the same of Washington.
*"good faith" and "reasonable" are legal terms with specific tests and judicial precedent around them
> Other companies have disclosed pay information in ways that make it difficult to draw comparisons. For instance, some firms are setting pay ranges that are specific to Colorado, hinting that the pay might not be the same elsewhere. Others are posting salaries with ranges of as much as $100,000 or more between the low and high ends. A pharmacist job posting at Walmart said applicants can make anywhere from $52,416 to $153,920 annually for the same job.
When Colorado did the same thing, the Colorado department of labor issued rules that required employers to use a "good-faith and reasonable* estimate" of the salary range. You can expect the same of Washington.
*"good faith" and "reasonable" are legal terms with specific tests and judicial precedent around them