{"record":{"id":"5ab229b3b6e437d8","repo":"evanw/esbuild","slug":"invalid-banner-file-type-type","errorCode":null,"errorMessage":"Invalid banner file type: ${type}","messagePattern":"Invalid banner file type: (.+?)","errorType":"validation","errorClass":"Error","httpStatus":null,"severity":"error","filePath":"lib/shared/common.ts","lineNumber":322,"sourceCode":"  if (tsconfig) flags.push(`--tsconfig=${tsconfig}`)\n  if (packages) flags.push(`--packages=${packages}`)\n  if (resolveExtensions) flags.push(`--resolve-extensions=${validateAndJoinStringArray(resolveExtensions, 'resolve extension')}`)\n  if (publicPath) flags.push(`--public-path=${publicPath}`)\n  if (entryNames) flags.push(`--entry-names=${entryNames}`)\n  if (chunkNames) flags.push(`--chunk-names=${chunkNames}`)\n  if (assetNames) flags.push(`--asset-names=${assetNames}`)\n  if (mainFields) flags.push(`--main-fields=${validateAndJoinStringArray(mainFields, 'main field')}`)\n  if (conditions) flags.push(`--conditions=${validateAndJoinStringArray(conditions, 'condition')}`)\n  if (external) for (let name of external) flags.push(`--external:${validateStringValue(name, 'external')}`)\n  if (alias) {\n    for (let old in alias) {\n      if (old.indexOf('=') >= 0) throw new Error(`Invalid package name in alias: ${old}`)\n      flags.push(`--alias:${old}=${validateStringValue(alias[old], 'alias', old)}`)\n    }\n  }\n  if (banner) {\n    for (let type in banner) {\n      if (type.indexOf('=') >= 0) throw new Error(`Invalid banner file type: ${type}`)\n      flags.push(`--banner:${type}=${validateStringValue(banner[type], 'banner', type)}`)\n    }\n  }\n  if (footer) {\n    for (let type in footer) {\n      if (type.indexOf('=') >= 0) throw new Error(`Invalid footer file type: ${type}`)\n      flags.push(`--footer:${type}=${validateStringValue(footer[type], 'footer', type)}`)\n    }\n  }\n  if (inject) for (let path of inject) flags.push(`--inject:${validateStringValue(path, 'inject')}`)\n  if (loader) {\n    for (let ext in loader) {\n      if (ext.indexOf('=') >= 0) throw new Error(`Invalid loader extension: ${ext}`)\n      flags.push(`--loader:${ext}=${validateStringValue(loader[ext], 'loader', ext)}`)\n    }\n  }\n  if (outExtension) {\n    for (let ext in outExtension) {","sourceCodeStart":304,"sourceCodeEnd":340,"githubUrl":"https://github.com/evanw/esbuild/blob/f6058f8364fe7ab91ca57a83e02577ed74c9cae4/lib/shared/common.ts#L304-L340","documentation":"The `banner` option (build) is a map of file type to text, serialized as `--banner:TYPE=TEXT`. An '=' inside the TYPE breaks parsing, so esbuild rejects it at lib/shared/common.ts:322. Valid types are typically 'js' and 'css'.","triggerScenarios":"Passing `banner: { 'js=x': '...' }` or any banner key containing '='.","commonSituations":"Typo or generated key; confusion about which key to use (should be 'js'/'css').","solutions":["Use a valid file type key without '=' (commonly 'js' or 'css').","Strip '=' from generated keys."],"exampleFix":"// before\nawait build({ entryPoints: ['app.ts'], banner: { 'js=app': '/* header */' } })\n\n// after\nawait build({ entryPoints: ['app.ts'], banner: { js: '/* header */' } })","handlingStrategy":"validation","validationCode":"const VALID_BANNER_TYPES = new Set(['js', 'css'])\nfunction assertBannerKeys(map) {\n  for (const k of Object.keys(map ?? {})) {\n    if (!VALID_BANNER_TYPES.has(k)) throw new Error(`banner key must be 'js' or 'css', got ${k}`)\n  }\n}\nassertBannerKeys(options.banner)","typeGuard":null,"tryCatchPattern":null,"preventionTips":["Restrict banner keys to 'js' or 'css'.","Don't embed '=' or filenames in banner keys.","Generate the banner text in the value, not the key."],"tags":["config","validation","banner"],"backgroundTag":null,"analyzedSha":"f6058f8364fe7ab91ca57a83e02577ed74c9cae4","analyzedAt":"2026-08-09T18:37:22.223Z","contentChangedAt":null,"schemaVersion":2},"datasetVersion":"2026-09-23T08:17:48.524Z"}