ESLint规则，每个文件仅允许默认或命名导出

Question

I wish to have a following ESLint rule:

A js file can have either one default export, or as many named exports as possible. But not both. So having one default export + named exports should result in an eslint warning. Is this possible with eslint currently? If not, would it be easy to make a rule like that?

Answer 1

Looking at the code for prefer-default-export , it looks like it may well be as simple as forking that rule and changing

'Program:exit': function() {
  if (specifierExportCount === 1 && !hasDefaultExport && !hasStarExport) {
    context.report(namedExportNode, 'Prefer default export.')
  }
},

to

'Program:exit': function() {
  if ((specifierExportCount >= 1 || hasStarExport) && hasDefaultExport) {
    context.report(namedExportNode, 'Do not use both named exports and a default export')
  }
},

specifierExportCount in that rule module counts the number of named exports.