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JavaScript could not decode or encode a malformed URI sequence

URIError: malformed URI sequence

JavaScript hit invalid percent-encoding or malformed Unicode data while processing a URI component.

URIError: malformed URI sequenceruntime

Observed message

URIError: malformed URI sequence

Why it happens

  • The URI contains invalid percent-encoded bytes.
  • User input or upstream data is not valid URI-encoded text.
  • Code decodes a string that was never encoded correctly in the first place.

How to fix it

  1. Validate URI input before decoding.
  2. Check for stray percent signs or incomplete escape sequences.
  3. Make sure the producer encodes values correctly before they are decoded.

Official reference

MDN: URIError: malformed URI sequence

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JavaScript malformed URI sequence: causes and fixes | Error Atlas