outputErrors

Use it to output a native Google Sheets #ERROR! message when an error occurs.

By default the function returns custom messages when an error occurs (such as #SELECTOR_NOT_VALID). Those messages are not recognized by Google Sheets as proper errors. Therefore you cannot use the ISERROR or IFERROR functions.

=IMPORTFROMWEB(data_sources, selectors, "outputErrors")

or

AB
1outputErrorsTRUE
3=IMPORTFROMWEB(data_sources, selectors, A1:B1)

#ERROR! messages can be handled with the ISERROR or IFERROR functions.

The downside of it is that the #ERROR! message displayed by Google Sheets doesn’t tell much about the type of error. Pass the mouse over the cell to see more information about the error.