vitest-dev/vitest · error · Error

Invalid data URI encoding

Error message

Invalid data URI encoding: ${encoding}

What it means

Thrown by parseDataUri (line 48) only for WebAssembly data URIs: the MIME is `application/wasm`, an encoding IS present, but it is not `base64`. Vitest supports exclusively base64-encoded wasm data URIs, so any other encoding value (e.g. `charset=utf-8`) for wasm is rejected here, before attempting to decode binary.

Solutions

1. Switch the encoding to base64 for wasm: `data:application/wasm;base64,...`.
2. If you have raw text you think is wasm, you likely need real binary bytes base64-encoded, not a text encoding.
3. Load wasm from a file URL to avoid encoding pitfalls entirely.

Example fix

// before
import wasm from 'data:application/wasm;charset=utf-8,...'

// after
import wasm from 'data:application/wasm;base64,<base64>'

function validWasmDataUri(uri: string): boolean {
  return /^data:application\/wasm;base64,.+$/.test(uri)
}

function isBase64WasmDataUri(uri: string): boolean {
  return /^data:application\/wasm;base64,[A-Za-z0-9+/=]+$/.test(uri)
}

When it happens

Trigger: Importing a wasm module via a data URI with a non-base64 encoding segment, e.g. `data:application/wasm;charset=utf-8,...`. This is invalid because wasm bytes cannot be represented as UTF-8 text in a URI.

Common situations: Mis-generating a wasm URI with the wrong encoding token; concatenating a JS-style `charset=utf-8` header onto a wasm payload; tooling that defaults all data URIs to the same encoding.

Related errors

• Missing data URI encoding
• Invalid data URI
• Cannot import " ": its vm context was torn down.
• invalid diff config file
• invalid snapshot serializer file

AI-assisted analysis of vitest-dev/vitest@1fa9837ec2 (2026-08-11). Data as JSON: /api/errors/9852ea8a9055fad6. Report an issue: GitHub.

Appendix: source

Thrown at packages/vitest/src/runtime/vm/esm-executor.ts:48

  return module instanceof SourceTextModule && module.hasAsyncGraph()
}

const dataURIRegex
  = /^data:(?<mime>text\/javascript|application\/json|application\/wasm)(?:;(?<encoding>charset=utf-8|base64))?,(?<code>.*)$/

function parseDataUri(identifier: string): { mime: string; code: string | Buffer } {
  const match = identifier.match(dataURIRegex)
  if (!match || !match.groups) {
    throw new Error('Invalid data URI')
  }
  const { mime, encoding } = match.groups
  let code: string | Buffer = match.groups.code
  if (mime === 'application/wasm') {
    if (!encoding) {
      throw new Error('Missing data URI encoding')
    }
    if (encoding !== 'base64') {
      throw new Error(`Invalid data URI encoding: ${encoding}`)
    }
    return { mime, code: Buffer.from(code, 'base64') }
  }
  if (!encoding || encoding === 'charset=utf-8') {
    code = decodeURIComponent(code)
  }
  else if (encoding === 'base64') {
    code = Buffer.from(code, 'base64').toString()
  }
  else {
    throw new Error(`Invalid data URI encoding: ${encoding}`)
  }
  return { mime, code }
}

function getContextExecutor(mod: VMModule): ExternalModulesExecutor {
  const vmContext = (mod.context as any)?.[VITEST_VM_CONTEXT_SYMBOL]
  if (!vmContext) {

View on GitHub (pinned to 1fa9837ec2)