Use CSS-like selectors to match nodes in an esprima abstract syntax tree (AST).

var eselector = require('esprima-selector');

If you're using a library like falafel, then you have a callback function that takes an AST node as its argument. Well, eselector.tester() accepts an array of such functions, each with a CSS-like selector for the nodes it should be called for. Example:

var eselector = require('esprima-selector');
var src = falafel(fs.readFileSync('test.js', 'utf8'), eselector.tester([
  {
    selector: '*',
    callback: function(node) {
      // Gets called for every node in the AST.
      console.log('node', node.name, node.classes);
    },
  },
  {
    selector: 'program',
    callback: function(node) {
      // Gets called for the outmost node in the AST.
      node.update(
          'var indent = []; function start() { console.log(indent.join(\'\') + \'*\'); indent.push(\'\t\') } function end() { indent.pop() }' +
          node.source());
    },
  },
  {
    selector: 'program declaration.function > block',
    callback: function(node) {
      // Gets called for every code block that's the body of a function
      // declaration.
      node.update('start();' + node.source() + 'end();');
    },
  },
]));

You select these as if they were CSS tags (ex: block > statement):

• program (the outermost node)
• expression (e.g. variable references, math expressions, initializers)
• statement (e.g. return, if(...) {...}, debugger)
• clause (e.g. catch(e) {...})
• block (e.g. {...})
• declaration (e.g. var x = ...)
• declarator (e.g. the x = ... part of var x = ...)
• property (e.g. the a: part of {a: 42})
• switch-case (e.g. case 42: ...)

You select these as if they were CSS classes (ex: .function or declaration.function):

• identifier (e.g. variable reference)
• literal (e.g. 42 or "foo")
• this
• call (e.g. a())
• unary (e.g. -i)
• update (e.g. i++)
• binary (e.g. a + b)
• array
• assignment
• member (e.g. a.b)
• logical (e.g. a && b)
• ternary (e.g. a ? b : c)
• comma (e.g. a, b)
• object
• new
• function
• return
• break
• label (e.g. foo:)
• expression
• if
• while
• do-while
• throw
• try
• catch
• for
• forin
• switch
• debugger
• variable
• branch (e.g. the {...} of if (...) {...})
• consequent (the first branch of an if statement)
• alternate (the else branch of an if statement)