evanw/esbuild · error · Error

Invalid package name in alias: ${old}

Error message

Invalid package name in alias: ${old}

What it means

Error "Invalid package name in alias: ${old}" thrown in evanw/esbuild.

Source

Thrown at lib/shared/common.ts:314

  if (splitting) flags.push('--splitting')
  if (preserveSymlinks) flags.push('--preserve-symlinks')
  if (metafile) flags.push(`--metafile`)
  if (outfile) flags.push(`--outfile=${outfile}`)
  if (outdir) flags.push(`--outdir=${outdir}`)
  if (outbase) flags.push(`--outbase=${outbase}`)
  if (tsconfig) flags.push(`--tsconfig=${tsconfig}`)
  if (packages) flags.push(`--packages=${packages}`)
  if (resolveExtensions) flags.push(`--resolve-extensions=${validateAndJoinStringArray(resolveExtensions, 'resolve extension')}`)
  if (publicPath) flags.push(`--public-path=${publicPath}`)
  if (entryNames) flags.push(`--entry-names=${entryNames}`)
  if (chunkNames) flags.push(`--chunk-names=${chunkNames}`)
  if (assetNames) flags.push(`--asset-names=${assetNames}`)
  if (mainFields) flags.push(`--main-fields=${validateAndJoinStringArray(mainFields, 'main field')}`)
  if (conditions) flags.push(`--conditions=${validateAndJoinStringArray(conditions, 'condition')}`)
  if (external) for (let name of external) flags.push(`--external:${validateStringValue(name, 'external')}`)
  if (alias) {
    for (let old in alias) {
      if (old.indexOf('=') >= 0) throw new Error(`Invalid package name in alias: ${old}`)
      flags.push(`--alias:${old}=${validateStringValue(alias[old], 'alias', old)}`)
    }
  }
  if (banner) {
    for (let type in banner) {
      if (type.indexOf('=') >= 0) throw new Error(`Invalid banner file type: ${type}`)
      flags.push(`--banner:${type}=${validateStringValue(banner[type], 'banner', type)}`)
    }
  }
  if (footer) {
    for (let type in footer) {
      if (type.indexOf('=') >= 0) throw new Error(`Invalid footer file type: ${type}`)
      flags.push(`--footer:${type}=${validateStringValue(footer[type], 'footer', type)}`)
    }
  }
  if (inject) for (let path of inject) flags.push(`--inject:${validateStringValue(path, 'inject')}`)
  if (loader) {
    for (let ext in loader) {

View on GitHub (pinned to 6ff1d8b0d8)

Solutions

1. Use a valid package name as the alias key (no subpaths or invalid characters in the package name position)
2. Fix the alias map so keys are plain package names

Example fix

esbuild.buildSync({ alias: { 'react': 'preact/compat' } });

When it happens

Trigger: Thrown at lib/shared/common.ts:314 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of evanw/esbuild@6ff1d8b0d8 (2026-08-03). Data as JSON: /data/errors/920a667dfc09a287.json. Report an issue: GitHub.