Many developers was wondering about the following line
What does the “double slashes” do or is this line of code correct?
It’s a relative URL without a scheme(http or https) according to RFC 3986: “Uniform Resource Identifier (URI): Generic Syntax”, Section 4.2. It’s useful when switching between http and https, because you won’t need to explicitly specify the scheme. It’s also supported in all web browsers.
More detailed, the two forward slashes are described as a common shorthand for whatever protocol being used