The Headers.forEach() method executes a callback function once per each key/value pair in the Headers object.

callbackFn

Function to execute for each entry in the map. It takes the following arguments:

value

Value of the currently visited header entry.

key

Name of the currently visited header entry.

object

The Headers object being iterated.

thisArg Optional

Value to use as this when executing callback.

undefined.

The Headers.forEach() method executes the provided callback once for each key of the Headers which actually exist. It is not invoked for keys which have been deleted. However, it is executed for keys which are present but have the value undefined.

The following code logs a line for each key/value in the myHeaders object.

// Create a new test Headers object
const myHeaders = new Headers();
myHeaders.append("Content-Type", "application/json");
myHeaders.append("Cookie", "This is a demo cookie");
myHeaders.append("compression", "gzip");

// Display the key/value pairs
myHeaders.forEach((value, key) => {
  console.log(`${key} ==> ${value}`);
});

The result is:

compression ==> gzip
content-type ==> application/json
cookie ==> This is a demo cookie

• Map.prototype.forEach()
• ServiceWorker API
• HTTP access control (CORS)
• HTTP