Initializers are not allowed in ambient contexts.

[cjmling]

https://stackoverflow.com/a/53139356/507203

[cjmling]

I guess it should be

private useFormat?: boolean
private useFormattedDate?: boolean

And only get default sets in constructor.

} else if (typeof option === 'string') {
      this.sheetName = option
      this.sheetId = this.sheetId || null
      this.useFormattedDate = false   <===
      this.useFormat = false <===
} else if (typeof option === 'object') {  

[fureweb-com]

Thanks for letting me know!
I've been on vacation and was late checking in.

I'll fix the offending type definition part soon and release it in the next version.

Thanks :)