A filter is used to modify some specified data. Hexo passes data to filters in sequence and the filters then modify the data one after the other. This concept was borrowed from WordPress.

Synopsis

hexo.extend.filter.register(type, function(){
  // ...
}, priority);

You can define the priority. Lower priority means that it will be executed first. The default priority is 10.

Execute Filters

hexo.extend.filter.exec(type, data, options);
hexo.extend.filter.execSync(type, data, options);

The first argument passed into each filter is data. The data passed into the next filter can be modified by returning a new value. If nothing is returned, the data remains unmodified. You can even use args to specify other arguments in filters. For example:

hexo.extend.filter.register('test', function(data, arg1, arg2){
  // data === 'some data'
  // arg1 === 'foo'
  // arg2 === 'bar'
  return 'something';
});
hexo.extend.filter.register('test', function(data, arg1, arg2){
  // data === 'something'
});
hexo.extend.filter.exec('test', 'some data', {
  args: ['foo', 'bar']
});

You can also use the following methods to execute filters:

hexo.execFilter(type, data, options);
hexo.execFilterSync(type, data, options);

Unregister Filters

hexo.extend.filter.unregister(type, filter);

Filter List

Here is a list of filters used by Hexo.

before_post_render

Executed before a post is rendered. Refer to post rendering to learn the execution steps.

For example, to transform the title to lower case:

hexo.extend.filter.register('before_post_render', function(data){
  data.title = data.title.toLowerCase();
  return data;
});

after_post_render

Executed after a post is rendered. Refer to post rendering to learn the execution steps.

For example, to replace @username with a link to a Twitter profile:

hexo.extend.filter.register('after_post_render', function(data){
  data.content = data.content.replace(/@(\d+)/, '<a href="http://twitter.com/$1">#$1</a>');
  return data;
});

before_exit

Executed before Hexo is about to exit – this will run right after hexo.exit is called.

hexo.extend.filter.register('before_exit', function(){
  // ...
});

before_generate

Executed before generation begins.

hexo.extend.filter.register('before_generate', function(){
  // ...
});

after_generate

Executed after generation finishes.

hexo.extend.filter.register('after_generate', function(){
  // ...
});

template_locals

Modify local variables in templates.

For example, to add the current time to the local variables of templates:

hexo.extend.filter.register('template_locals', function(locals){
  locals.now = Date.now();
  return locals;
});

after_init

Executed after Hexo is initialized – this will run right after hexo.init completes.

hexo.extend.filter.register('after_init', function(){
  // ...
});

new_post_path

Executed when creating a post to determine the path of new posts.

hexo.extend.filter.register('new_post_path', function(data, replace){
  // ...
});

post_permalink

Used to determine the permalink of posts.

hexo.extend.filter.register('post_permalink', function(data){
  // ...
});

after_render

Executed after rendering finishes. You can see rendering for more info.

server_middleware

Add middleware to the server. app is a Connect instance.

For example, to add X-Powered-By: Hexo to the response header:

hexo.extend.filter.register('server_middleware', function(app){
  app.use(function(req, res, next){
    res.setHeader('X-Powered-By', 'Hexo');
    next();
  });
});