transloadit/uppy · error · Error

isDropOrPaste must be either 'drop' or 'paste', but it's

Error message

isDropOrPaste must be either 'drop' or 'paste', but it's ${isDropOrPaste}

What it means

forEachDroppedOrPastedUrl's switch on isDropOrPaste hit its default case, meaning the caller passed something other than the literal strings 'drop' or 'paste'. It is a programming-error guard for the internal API's discriminant parameter.

Solutions

Pass exactly 'drop' from drop handlers and 'paste' from paste handlers
If you don't control the string, narrow it before calling: only invoke when value === 'drop' || value === 'paste'

Example fix

// before
forEachDroppedOrPastedUrl(event, cb, 'dragover')
// after
forEachDroppedOrPastedUrl(event, cb, 'drop')

Defensive patterns

Strategy: type-guard

Validate before calling

if (kind !== 'drop' && kind !== 'paste') return

Type guard

const isDropOrPaste = (v: string): v is 'drop' | 'paste' => v === 'drop' || v === 'paste'

Prevention

Type the parameter as 'drop' | 'paste' in your own wrappers
Derive the value from the event.type rather than hardcoding strings

When it happens

Trigger: Calling forEachDroppedOrPastedUrl(event, cb, 'dragover' | 'input' | undefined | anyOtherValue) instead of 'drop' or 'paste'.

Common situations: Custom integrations or forks invoking the util directly with a wrong event-type string; typos like 'drops' or 'Drop'.

Understand the failure class

Background: "invalid argument", "unknown mode", "not supported": invalid enum-like argument errors explained — this error's family across 19 libraries.

Related errors

AI-assisted analysis of transloadit/uppy@5d4dedd02a (2026-08-28). Data as JSON: /api/errors/fe552d401b50bca2. Report an issue: GitHub.

Appendix: source

Thrown at packages/@uppy/url/src/utils/forEachDroppedOrPastedUrl.ts:85

    case 'paste': {
      const atLeastOneFileIsDragged = items.some((item) => item.kind === 'file')
      if (atLeastOneFileIsDragged) {
        return
      }
      urlItems = items.filter(
        (item) => item.kind === 'string' && item.type === 'text/plain',
      )

      break
    }
    case 'drop': {
      urlItems = items.filter(
        (item) => item.kind === 'string' && item.type === 'text/uri-list',
      )
      break
    }
    default: {
      throw new Error(
        `isDropOrPaste must be either 'drop' or 'paste', but it's ${isDropOrPaste}`,
      )
    }
  }

  urlItems.forEach((item) => {
    item.getAsString((urlString) => callback(urlString))
  })
}

View on GitHub (pinned to 5d4dedd02a)