React Native

Get a MIME Header Field Value

Demonstrates the Chilkat Mime.GetHeaderField method, which returns the value of the first header field whose name matches case-insensitively. The only argument is the field name; it returns null when no matching field exists.

Note: The file path is relative to the application's current working directory. Absolute paths may also be used. Supply the path to your own file.

Background: This is the everyday way to read a header value — the Subject, a Message-ID, a custom X- header. Because a missing field returns null, the returned value is assigned to a variable and checked rather than used directly, so an absent header is handled cleanly instead of surfacing as an error later. Only the first matching occurrence is returned; iterate by index to see duplicates.

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React Native

import { Mime } from '@chilkat/react-native'

function chilkatExample() {
  const mime = new Mime();
  try {
    mime.loadMimeFile('qa_data/message.eml');
  } catch {
    console.log(mime.lastErrorText);
    return;
  }

  // Return the value of the first header field with a matching (case-insensitive) name.
  // GetHeaderField returns null when no matching field exists, so assign it to a string variable
  // and check for success.
  let subject: string;
  try {
    subject = mime.getHeaderField('Subject');
  } catch {
    console.log(mime.lastErrorText);
    return;
  }

  console.log(`Subject: ${subject}`);
}