egoist · egoist · Nov 12, 2021 · Nov 7, 2021 · Nov 12, 2021 · Nov 12, 2021
diff --git a/docs/README.md b/docs/README.md
@@ -68,34 +68,35 @@ You can use any of these files:
 
 [Check out all available options](https://github.com/egoist/tsup/blob/master/src/options.ts).
 
-#### TypeScript
+#### TypeScript / JavaScript
 
 ```ts
-// tsup.config.ts
-import type { Options } from 'tsup'
-export const tsup: Options = {
+import { defineConfig } from 'tsup'
+
+export default defineConfig({
   splitting: false,
   sourcemap: true,
   clean: true,
   entryPoints: ['src/index.ts'],
-}
+})
 ```
 
-#### JavaScript
+#### Conditional config
 
-```js
-// tsup.config.cjs
-/**
- * @type {import("tsup").Options}
- */
-module.exports = {
-  splitting: false,
-  sourcemap: true,
-  clean: true,
-  entryPoints: ['src/index.ts'],
-}
+If the config needs to be conditionally determined based on CLI flags, it can export a function instead:
+
+```ts
+import { defineConfig } from 'tsup'
+
+export default defineConfig((options) => {
+  return {
+    minify: !options.watch,
+  }
+})
 ```
 
+The `options` here is derived from CLI flags.
+
 #### package.json
 
 ```json
@@ -290,14 +291,14 @@ The file outputs as `metafile-{format}.json`, e.g. `tsup --format cjs,esm` will
 Use `esbuildPlugins` and `esbuildOptions` respectively in `tsup.config.ts`:
 
 ```ts
-import { Options } from 'tsup'
+import { defineConfig } from 'tsup'
 
-export const tsup: Options = {
+export default defineConfig({
   esbuildPlugins: [YourPlugin],
   esbuildOptions(options, context) {
     options.define.foo = '"bar"'
   },
-}
+})
 ```
 
 The `context` argument for `esbuildOptions`:

diff --git a/src/cli-main.ts b/src/cli-main.ts
@@ -73,7 +73,7 @@ export async function main(options: Options = {}) {
     .option('--clean', 'Clean output directory')
     .option(
       '--silent',
-      'Supress non-error logs (excluding "onSuccess" process output)'
+      'Suppress non-error logs (excluding "onSuccess" process output)'
     )
     .option('--pure <express>', 'Mark specific expressions as pure')
     .option('--metafile', 'Emit esbuild metafile (a JSON file)')

diff --git a/src/esbuild/postcss.ts b/src/esbuild/postcss.ts
@@ -66,7 +66,7 @@ export const postcssPlugin = ({
           }
         }
 
-        // Tranform CSS
+        // Transform CSS
         const result = await postcss
           ?.default(plugins)
           .process(contents, { ...options, from: args.path })

diff --git a/src/index.ts b/src/index.ts
@@ -54,7 +54,14 @@ const getOutputExtensionMap = (
   return map
 }
 
-export const defineConfig = (options: Options) => options
+export const defineConfig = (
+  options:
+    | Options
+    | ((
+        /** The options derived from CLI flags */
+        overrideOptions: Options
+      ) => Options)
+) => options
 
 export async function runEsbuild(
   options: NormalizedOptions,
@@ -239,7 +246,7 @@ export async function runEsbuild(
               )
             }
           }
-          // Workaound to enable code splitting for cjs format
+          // Workaround to enable code splitting for cjs format
           // Manually transform esm to cjs
           // TODO: remove this once esbuild supports code splitting for cjs natively
           if (splitting && format === 'cjs') {
@@ -282,7 +289,7 @@ const killProcess = ({
   })
 
 const normalizeOptions = async (
-  optionsFromConfigFile: Options,
+  optionsFromConfigFile: Options | undefined,
   optionsOverride: Options
 ) => {
   const options: Buildable<NormalizedOptions> = {
@@ -344,7 +351,10 @@ const normalizeOptions = async (
 export async function build(_options: Options) {
   const config = await loadTsupConfig(process.cwd())
 
-  const options = await normalizeOptions(config.data, _options)
+  const configData =
+    typeof config.data === 'function' ? config.data(_options) : config.data
+
+  const options = await normalizeOptions(configData, _options)
 
   log('CLI', 'info', `tsup v${version}`)
 

diff --git a/src/options.ts b/src/options.ts
@@ -69,7 +69,7 @@ export type Options = {
   esbuildPlugins?: EsbuildPlugin[]
   esbuildOptions?: (options: BuildOptions, context: { format: Format }) => void
   /**
-   * Supress non-error logs (excluding "onSuccess" process output)
+   * Suppress non-error logs (excluding "onSuccess" process output)
    */
   silent?: boolean
   /**

diff --git a/src/rollup.ts b/src/rollup.ts
@@ -49,10 +49,10 @@ const findLowestCommonAncestor = (filepaths: string[]) => {
 // See #316
 const toObjectEntry = (entry: string[]) => {
   entry = entry.map((e) => e.replace(/\\/g, '/'))
-  const ancester = findLowestCommonAncestor(entry)
+  const ancestor = findLowestCommonAncestor(entry)
   return entry.reduce((result, item) => {
     const key = item
-      .replace(ancester, '')
+      .replace(ancestor, '')
       .replace(/^\//, '')
       .replace(/\.[a-z]+$/, '')
     return {

diff --git a/src/rollup/ts-resolve.ts b/src/rollup/ts-resolve.ts
@@ -52,7 +52,7 @@ export const tsResolvePlugin: PluginImpl<TsResolveOptions> = ({
         if (!shouldResolve) return null
       }
 
-      // Skip absolut path
+      // Skip absolute path
       if (path.isAbsolute(source)) return null
 
       const basedir = importer ? path.dirname(importer) : process.cwd()