diff --git a/js/dom_types.ts b/js/dom_types.ts
index e1fa235bb3..e3f75e4886 100644
--- a/js/dom_types.ts
+++ b/js/dom_types.ts
@@ -13,7 +13,8 @@ See the Apache Version 2.0 License for specific language governing permissions
 and limitations under the License.
 *******************************************************************************/
 
-export type HeadersInit = string[][] | Record<string, string>;
+export type HeadersInit = Headers | string[][] | Record<string, string>;
+export type URLSearchParamsInit = string | string[][] | Record<string, string>;
 type BodyInit =
   | Blob
   | BufferSource
@@ -74,7 +75,7 @@ export interface ProgressEventInit extends EventInit {
   total?: number;
 }
 
-interface URLSearchParams {
+export interface URLSearchParams {
   /**
    * Appends a specified key/value pair as a new search parameter.
    */
@@ -101,7 +102,20 @@ interface URLSearchParams {
    * If there were several values, delete the others.
    */
   set(name: string, value: string): void;
+  /**
+   * Sort all key/value pairs contained in this object in place 
+   * and return undefined. The sort order is according to Unicode 
+   * code points of the keys.
+   */
   sort(): void;
+  /**
+   * Returns a query string suitable for use in a URL.
+   */
+  toString(): string;
+  /** 
+   * Iterates over each name-value pair in the query 
+   * and invokes the given function.
+   */
   forEach(
     callbackfn: (value: string, key: string, parent: URLSearchParams) => void,
     // tslint:disable-next-line:no-any
diff --git a/js/fetch.ts b/js/fetch.ts
index 48429ca19c..9cf117ed8f 100644
--- a/js/fetch.ts
+++ b/js/fetch.ts
@@ -22,85 +22,86 @@ import {
 import { TextDecoder } from "./text_encoding";
 import { DenoBlob } from "./blob";
 
-interface Header {
-  name: string;
-  value: string;
-}
-
+// ref: https://fetch.spec.whatwg.org/#dom-headers
 export class DenoHeaders implements Headers {
-  private readonly headerList: Header[] = [];
+  private headerMap: Map<string, string> = new Map();
 
   constructor(init?: HeadersInit) {
-    if (init) {
-      this._fill(init);
+    if (arguments.length === 0 || init === undefined) {
+      return;
     }
-  }
 
-  private _append(header: Header): void {
-    // TODO(qti3e) Check header based on the fetch spec.
-    this._appendToHeaderList(header);
-  }
-
-  private _appendToHeaderList(header: Header): void {
-    const lowerCaseName = header.name.toLowerCase();
-    for (let i = 0; i < this.headerList.length; ++i) {
-      if (this.headerList[i].name.toLowerCase() === lowerCaseName) {
-        header.name = this.headerList[i].name;
-      }
-    }
-    this.headerList.push(header);
-  }
-
-  private _fill(init: HeadersInit): void {
-    if (Array.isArray(init)) {
-      for (let i = 0; i < init.length; ++i) {
-        const header = init[i];
-        if (header.length !== 2) {
+    if (init instanceof DenoHeaders) {
+      // init is the instance of Header
+      init.forEach((value: string, name: string) => {
+        this.headerMap.set(name, value);
+      });
+    } else if (Array.isArray(init)) {
+      // init is a sequence
+      init.forEach(item => {
+        if (item.length !== 2) {
           throw new TypeError("Failed to construct 'Headers': Invalid value");
         }
-        this._append({
-          name: header[0],
-          value: header[1]
-        });
-      }
+        const [name, value] = this.normalizeParams(item[0], item[1]);
+        const v = this.headerMap.get(name);
+        const str = v ? `${v}, ${value}` : value;
+        this.headerMap.set(name, str);
+      });
+    } else if (Object.prototype.toString.call(init) === "[object Object]") {
+      // init is a object
+      const names = Object.keys(init);
+      names.forEach(name => {
+        const value = (init as Record<string, string>)[name];
+        const [newname, newvalue] = this.normalizeParams(name, value);
+        this.headerMap.set(newname, newvalue);
+      });
     } else {
-      for (const key in init) {
-        this._append({
-          name: key,
-          value: init[key]
-        });
-      }
+      throw new TypeError("Failed to construct 'Headers': Invalid value");
     }
   }
 
+  private normalizeParams(name: string, value?: string): string[] {
+    name = String(name).toLowerCase();
+    value = String(value).trim();
+    return [name, value];
+  }
+
   append(name: string, value: string): void {
-    this._appendToHeaderList({ name, value });
+    const [newname, newvalue] = this.normalizeParams(name, value);
+    const v = this.headerMap.get(newname);
+    const str = v ? `${v}, ${newvalue}` : newvalue;
+    this.headerMap.set(newname, str);
   }
 
   delete(name: string): void {
-    assert(false, "Implement me");
+    const [newname] = this.normalizeParams(name);
+    this.headerMap.delete(newname);
   }
+
   get(name: string): string | null {
-    for (const header of this.headerList) {
-      if (header.name.toLowerCase() === name.toLowerCase()) {
-        return header.value;
-      }
-    }
-    return null;
+    const [newname] = this.normalizeParams(name);
+    const value = this.headerMap.get(newname);
+    return value || null;
   }
+
   has(name: string): boolean {
-    assert(false, "Implement me");
-    return false;
+    const [newname] = this.normalizeParams(name);
+    return this.headerMap.has(newname);
   }
+
   set(name: string, value: string): void {
-    assert(false, "Implement me");
+    const [newname, newvalue] = this.normalizeParams(name, value);
+    this.headerMap.set(newname, newvalue);
   }
+
   forEach(
     callbackfn: (value: string, key: string, parent: Headers) => void,
     // tslint:disable-next-line:no-any
     thisArg?: any
   ): void {
-    assert(false, "Implement me");
+    this.headerMap.forEach((value, name) => {
+      callbackfn(value, name, this);
+    });
   }
 }
 
diff --git a/js/fetch_test.ts b/js/fetch_test.ts
index 25d8c2ed01..9d76cb6ba4 100644
--- a/js/fetch_test.ts
+++ b/js/fetch_test.ts
@@ -43,3 +43,129 @@ testPerm({ net: true }, async function fetchBlob() {
   assertEqual(blob.type, headers.get("Content-Type"));
   assertEqual(blob.size, Number(headers.get("Content-Length")));
 });
+
+// Logic heavily copied from web-platform-tests, make 
+// sure pass mostly header basic test
+/* tslint:disable-next-line:max-line-length */
+// ref: https://github.com/web-platform-tests/wpt/blob/7c50c216081d6ea3c9afe553ee7b64534020a1b2/fetch/api/headers/headers-basic.html
+/* tslint:disable:no-unused-expression */
+test(function newHeaderTest() {
+  new Headers();
+  new Headers(undefined);
+  new Headers({});
+  try {
+    new Headers(null);
+  } catch (e) {
+    assertEqual(e.message, "Failed to construct 'Headers': Invalid value");
+  }
+
+  try {
+    const init = [["a", "b", "c"]];
+    new Headers(init);
+  } catch (e) {
+    assertEqual(e.message, "Failed to construct 'Headers': Invalid value");
+  }
+});
+
+const headerDict = {
+  "name1": "value1",
+  "name2": "value2",
+  "name3": "value3",
+  "name4": undefined,
+  "Content-Type": "value4"
+};
+const headerSeq = [];
+for (const name in headerDict) {
+  headerSeq.push([name, headerDict[name]]);
+}
+  
+test(function newHeaderWithSequence() {
+  const headers = new Headers(headerSeq);
+  for (const name in headerDict) {
+    assertEqual(headers.get(name), String(headerDict[name]));
+  }
+  assertEqual(headers.get("length"), null);
+});
+
+test(function newHeaderWithRecord() {
+  const headers = new Headers(headerDict);
+  for (const name in headerDict) {
+    assertEqual(headers.get(name), String(headerDict[name]));
+  }
+});
+
+test(function newHeaderWithHeadersInstance() {
+  const headers = new Headers(headerDict);
+  const headers2 = new Headers(headers);
+  for (const name in headerDict) {
+    assertEqual(headers2.get(name), String(headerDict[name]));
+  }
+});
+
+test(function headerAppendSuccess() {
+  const headers = new Headers();
+  for (const name in headerDict) {
+    headers.append(name, headerDict[name]);
+    assertEqual(headers.get(name), String(headerDict[name]));
+  }
+});
+
+test(function headerSetSuccess() {
+  const headers = new Headers();
+  for (const name in headerDict) {
+    headers.set(name, headerDict[name]);
+    assertEqual(headers.get(name), String(headerDict[name]));
+  }
+});
+
+test(function headerHasSuccess() {
+  const headers = new Headers(headerDict);
+  for (const name in headerDict) {
+    assert(headers.has(name), "headers has name " + name);
+    /* tslint:disable-next-line:max-line-length */
+    assert(!headers.has("nameNotInHeaders"), "headers do not have header: nameNotInHeaders");
+  }
+});
+
+test(function headerDeleteSuccess() {
+  const headers = new Headers(headerDict);
+  for (const name in headerDict) {
+    assert(headers.has(name), "headers have a header: " + name);
+    headers.delete(name);
+    assert(!headers.has(name), "headers do not have anymore a header: " + name);
+  }
+});
+
+test(function headerGetSuccess() {
+  const headers = new Headers(headerDict);
+  for (const name in headerDict) {
+    assertEqual(headers.get(name), String(headerDict[name]));
+    assertEqual(headers.get("nameNotInHeaders"), null);
+  }
+});
+
+const headerEntriesDict = {
+  "name1": "value1",
+  "Name2": "value2",
+  "name": "value3",
+  "content-Type": "value4",
+  "Content-Typ": "value5",
+  "Content-Types": "value6"
+};
+
+test(function headerForEachSuccess() {
+  const headers = new Headers(headerEntriesDict);
+  const keys = Object.keys(headerEntriesDict);
+  keys.forEach(key => {
+    const value = headerEntriesDict[key];
+    const newkey = key.toLowerCase();
+    headerEntriesDict[newkey] = value;
+  });
+  let callNum = 0;
+  headers.forEach((value, key, container) => {
+    assertEqual(headers, container);
+    assertEqual(value, headerEntriesDict[key]);
+    callNum++;
+  });
+  assertEqual(callNum, keys.length);
+});