diff --git a/.eslintignore b/.eslintignore
index 32e68a98cdc..6e9d3966136 100644
--- a/.eslintignore
+++ b/.eslintignore
@@ -1,3 +1,4 @@
 test/*/samples/**/*.js
 !test/*/samples/**/_config.js
 test/leak/index.js
+**/*.ts
\ No newline at end of file
diff --git a/cli/run/build.ts b/cli/run/build.ts
index cc8b01d9985..ec2e5abe104 100644
--- a/cli/run/build.ts
+++ b/cli/run/build.ts
@@ -1,7 +1,7 @@
 import ms from 'pretty-ms';
 import tc from 'turbocolor';
 import * as rollup from '../../src/node-entry';
-import { InputOptions, OutputAsset, OutputChunk, OutputOptions, RollupBuild, SourceMap } from '../../src/rollup/types';
+import { InputOptions, OutputOptions, RollupBuild, SourceMap } from '../../src/rollup/types';
 import relativeId from '../../src/utils/relativeId';
 import { handleError, stderr } from '../logging';
 import SOURCEMAPPING_URL from '../sourceMappingUrl';
@@ -49,12 +49,12 @@ export default function build(
 				return bundle.generate(output).then(({ output: outputs }) => {
 					for (const file of outputs) {
 						let source: string | Buffer;
-						if ((file as OutputAsset).isAsset) {
-							source = (file as OutputAsset).source;
+						if (file.type === 'asset') {
+							source = file.source;
 						} else {
-							source = (file as OutputChunk).code;
+							source = file.code;
 							if (output.sourcemap === 'inline') {
-								source += `\n//# ${SOURCEMAPPING_URL}=${((file as OutputChunk)
+								source += `\n//# ${SOURCEMAPPING_URL}=${(file
 									.map as SourceMap).toUrl()}\n`;
 							}
 						}
diff --git a/docs/02-javascript-api.md b/docs/02-javascript-api.md
index 634638372f9..06471e94a99 100755
--- a/docs/02-javascript-api.md
+++ b/docs/02-javascript-api.md
@@ -25,12 +25,13 @@ async function build() {
   const { output } = await bundle.generate(outputOptions);
 
   for (const chunkOrAsset of output) {
-    if (chunkOrAsset.isAsset) {
+    if (chunkOrAsset.type === 'asset') {
       // For assets, this contains
       // {
-      //   isAsset: true,                 // signifies that this is an asset
+      //   isAsset: true,                 // signifies that this is an asset, !deprecated use type === asset instead
       //   fileName: string,              // the asset file name
       //   source: string | Buffer        // the asset source
+      //   type: 'asset'
       // }
       console.log('Asset', chunkOrAsset);
     } else {
@@ -54,6 +55,7 @@ async function build() {
       //     };
       //   },
       //   name: string                   // the name of this chunk as used in naming patterns
+      //   type: 'chunk',
       // }
       console.log('Chunk', chunkOrAsset.modules);
     }
diff --git a/docs/05-plugin-development.md b/docs/05-plugin-development.md
index e42309a8ad3..5f2f4177d22 100644
--- a/docs/05-plugin-development.md
+++ b/docs/05-plugin-development.md
@@ -123,8 +123,9 @@ Called at the end of `bundle.generate()` or immediately before the files are wri
 // AssetInfo
 {
   fileName: string,
-  isAsset: true,
-  source: string | Buffer
+  isAsset: true, // deprecated
+  source: string | Buffer,
+  type: 'asset',
 }
 
 // ChunkInfo
@@ -146,7 +147,8 @@ Called at the end of `bundle.generate()` or immediately before the files are wri
       originalLength: number
     },
   },
-  name: string
+  name: string,
+  type: 'chunk',
 }
 ```
 
diff --git a/package-lock.json b/package-lock.json
index 2d4ed90320b..ea09d24fd56 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1614,9 +1614,9 @@
       }
     },
     "eslint-utils": {
-      "version": "1.4.0",
-      "resolved": "https://registry.npmjs.org/eslint-utils/-/eslint-utils-1.4.0.tgz",
-      "integrity": "sha512-7ehnzPaP5IIEh1r1tkjuIrxqhNkzUJa9z3R92tLJdZIVdWaczEhr3EbhGtsMrVxi1KeR8qA7Off6SWc5WNQqyQ==",
+      "version": "1.4.2",
+      "resolved": "https://registry.npmjs.org/eslint-utils/-/eslint-utils-1.4.2.tgz",
+      "integrity": "sha512-eAZS2sEUMlIeCjBeubdj45dmBHQwPHWyBcT1VSYB7o9x9WRRqKxyUoiXlRjyAwzN7YEzHJlYg0NmzDRWx6GP4Q==",
       "dev": true,
       "requires": {
         "eslint-visitor-keys": "^1.0.0"
diff --git a/src/rollup/index.ts b/src/rollup/index.ts
index 4f0246b0f54..10e04a91ee1 100644
--- a/src/rollup/index.ts
+++ b/src/rollup/index.ts
@@ -166,6 +166,7 @@ function assignChunksToBundle(
 			isEntry: facadeModule !== null && facadeModule.isEntryPoint,
 			map: undefined,
 			modules: chunk.renderedModules,
+			type: 'chunk',
 			get name() {
 				return chunk.getChunkName();
 			}
@@ -301,7 +302,7 @@ export default async function rollup(rawInputOptions: GenericConfigObject): Prom
 				let chunkCnt = 0;
 				for (const fileName of Object.keys(bundle)) {
 					const file = bundle[fileName];
-					if ((file as OutputAsset).isAsset) continue;
+					if (file.type === 'asset') continue;
 					chunkCnt++;
 					if (chunkCnt > 1) break;
 				}
@@ -343,10 +344,10 @@ enum SortingFileType {
 }
 
 function getSortingFileType(file: OutputAsset | OutputChunk): SortingFileType {
-	if ((file as OutputAsset).isAsset) {
+	if (file.type === 'asset') {
 		return SortingFileType.ASSET;
 	}
-	if ((file as OutputChunk).isEntry) {
+	if (file.isEntry) {
 		return SortingFileType.ENTRY_CHUNK;
 	}
 	return SortingFileType.SECONDARY_CHUNK;
@@ -368,7 +369,7 @@ function createOutput(outputBundle: Record<string, OutputChunk | OutputAsset | {
 }
 
 function isOutputAsset(file: OutputAsset | OutputChunk): file is OutputAsset {
-	return (file as OutputAsset).isAsset === true;
+	return file.type === 'asset';
 }
 
 function writeOutputFile(
diff --git a/src/rollup/types.d.ts b/src/rollup/types.d.ts
index f24e305b4d7..89e7a65d83a 100644
--- a/src/rollup/types.d.ts
+++ b/src/rollup/types.d.ts
@@ -314,8 +314,13 @@ export interface OutputBundle {
 	[fileName: string]: OutputAsset | OutputChunk;
 }
 
+export interface FilePlaceholder {
+	isPlaceholder: true;
+	type: 'placeholder';
+}
+
 export interface OutputBundleWithPlaceholders {
-	[fileName: string]: OutputAsset | OutputChunk | {};
+	[fileName: string]: OutputAsset | OutputChunk | FilePlaceholder;
 }
 
 interface OnGenerateOptions extends OutputOptions {
@@ -487,9 +492,10 @@ export interface SerializedTimings {
 }
 
 export interface OutputAsset {
+	type: 'asset';
 	code?: undefined;
 	fileName: string;
-	isAsset: true;
+	isAsset: true; // deprecated
 	source: string | Buffer;
 }
 
@@ -518,6 +524,7 @@ export interface RenderedChunk extends PreRenderedChunk {
 }
 
 export interface OutputChunk extends RenderedChunk {
+	type: 'chunk';
 	code: string;
 	map?: SourceMap;
 }
diff --git a/src/utils/FileEmitter.ts b/src/utils/FileEmitter.ts
index edd72dda3ba..590d6e8f615 100644
--- a/src/utils/FileEmitter.ts
+++ b/src/utils/FileEmitter.ts
@@ -2,7 +2,7 @@ import sha256 from 'hash.js/lib/hash/sha/256';
 import Chunk from '../Chunk';
 import Graph from '../Graph';
 import Module from '../Module';
-import { OutputAsset, OutputBundleWithPlaceholders } from '../rollup/types';
+import { FilePlaceholder, OutputBundleWithPlaceholders } from '../rollup/types';
 import { BuildPhase } from './buildPhase';
 import {
 	errAssetNotFinalisedForFileName,
@@ -78,8 +78,9 @@ interface EmittedFile {
 
 type ConsumedFile = ConsumedChunk | ConsumedAsset;
 
-export const FILE_PLACEHOLDER = {
-	isPlaceholder: true
+export const FILE_PLACEHOLDER: FilePlaceholder = {
+	isPlaceholder: true,
+	type: 'placeholder'
 };
 
 function hasValidType(
@@ -318,7 +319,12 @@ export class FileEmitter {
 		// We must not modify the original assets to avoid interaction between outputs
 		const assetWithFileName = { ...consumedFile, source, fileName };
 		this.filesByReferenceId.set(referenceId, assetWithFileName);
-		output.bundle[fileName] = { fileName, isAsset: true, source };
+		output.bundle[fileName] = {
+			fileName,
+			isAsset: true, // deprecated
+			source,
+			type: 'asset'
+		};
 	}
 
 	private findExistingAssetFileNameWithSource(
@@ -326,9 +332,9 @@ export class FileEmitter {
 		source: string | Buffer
 	): string | null {
 		for (const fileName of Object.keys(bundle)) {
-			const outputFile = bundle[fileName] as OutputAsset;
+			const outputFile = bundle[fileName];
 			if (
-				outputFile.isAsset &&
+				outputFile.type === 'asset' &&
 				(Buffer.isBuffer(source) && Buffer.isBuffer(outputFile.source)
 					? source.equals(outputFile.source)
 					: source === outputFile.source)
diff --git a/test/form/samples/emit-asset-file/_config.js b/test/form/samples/emit-asset-file/_config.js
index ae942ca0d5e..68199c513c9 100644
--- a/test/form/samples/emit-asset-file/_config.js
+++ b/test/form/samples/emit-asset-file/_config.js
@@ -27,6 +27,7 @@ module.exports = {
 				const asset = outputBundle[keys[0]];
 				assert.strictEqual(asset.fileName, 'assets/logo-25585ac1.svg');
 				assert.strictEqual(asset.isAsset, true);
+				assert.strictEqual(asset.type, 'asset');
 				assert.ok(
 					asset.source.equals(fs.readFileSync(path.resolve(__dirname, 'logo.svg'))),
 					'asset has correct source'