JSLint will throw the "Expected exactly one space between '{a}' and '{b}'" error when it encounters a number of spaces that is not equal to one in the following situations (there are numerous other examples that can cause this error, but these are some of the common ones):
This error is raised to highlight a lack of convention and a possibly sloppy coding style. Your code will run without error if you do not change it, but may contravene best practices and look messy to other developers.
If you are happy with your coding style, you can tell JSLint to ignore whitespace (or the lack of whitespace) by setting the white option to true:
However, if you are using JSLint to enforce a consistent style, you will probably want to listen to what the error tells you, and just make sure you always use the correct whitespace: