Briefly compare setHeader and writeHead in Node and talk about the differences.

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Today when I was learning Node I found that setHeader and writeHead in Node/http are very similar. They can both set response headers. Let’s talk about it in detail!

setHeader

parameters

response.setHeader(name, value)Copy code

• name attribute
• value attribute value
• return http.ServerResponse returns the response object

and

sets a single attribute for the response header.

Note that

• you can only set properties one by one.

• Repeatedly setting a property will replace the previous setting.

• Property field names or values ​​containing invalid characters will cause TypeError to be thrown.

Example

response.setHeader('Content-Type', 'text/html')

response. setHeader('Set-Cookie', ['type=ninja', 'language=javascript'])

repeatedly sets an attribute

// returns content-type = text/html1
response.setHeader('Content-Type', 'text/html')
response.setHeader('Content-Type', 'text/html1')

writeHead

parameter

response.writeHead(statusCode, [statusMessage], [headers])

• statusCode http status code

• statusMessage status message (optional)

• headers | attribute object or array (optional)

• return http.ServerResponse return response object

The function

is the same as that setHeader

Note

• that multiple properties can be set. setHeader can only set one

• and can only be called once.

• It must be called before response.end()

• Setting the property field name or value containing invalid characters will cause TypeError to be thrown.

Example

because writeHead returns It is a ServerResponse object, we can make chain calls

const body = 'hello world';
response
  .writeHead(200, {
    'Content-Length': Buffer.byteLength(body),
    'Content-Type': 'text/plain'
  })
  .end(body);

Content-Length here is in bytes, not characters. Buffer.byteLength() is used to determine the length of the text.

Nodejs will not check whether Content-Length is consistent with the length of the transmitted text.

Use setHeader and writeHead at the same time

// Return content-type = text/plain
const server = http.createServer((req, res) => {
  res.setHeader('Content-Type', 'text/html');
  res.setHeader('X-Foo', 'bar');
  res.writeHead(200, { 'Content-Type': 'text/plain' });
  res.end('ok');
});

writeHead has a higher priority than setHeader , and writeHead can only be called once, so when calling, first consider which headers do not change often, and then call writeHead

If setHeader has been called to set the header, then he will pass it to writeHead merge

If this method is called and response.setHeader() has not been called), the provided header value will be written directly to the network channel and will not be cached internally. response.getHeader() ) on the header does not produce the expected results. If the header needs to be populated incrementally and potentially retrieved and modified in the future, use response.setHeader() instead.

Summary:

• setHeader can only set headers one by one, writeHead can set many

• setHeaders at once, and can be called repeatedly. writeHead can only be called once, and

• setHeader and writeHead appear at the same time. setHeader will be merged into writeHead, and writeHead has a high priority.

• writeHead can set status codes and status information. , setHeader cannot be set, only the header can be set