This is a lint error, caused by this lint rule: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-namespace.md
If you find the rule useful and want to keep it, then you’ll need to modify your code to use import and export instead of namespace. See the documentation of the rule for what counts as a fix.
If you like the rule, but want to disable the rule for this line, add the following just above it:
// eslint-disable-next-line @typescript-eslint/no-namespace
If you don’t like the rule and want to disable it entirely, then edit your .eslintrc file to have the following line:
rules: {
"@typescript-eslint/no-namespace": "off"
}