remove context argument

The optional `context` argument does not add any substantial utility
(beyond `Function.prototype.bind` or fat arrows) to warrant
the monstrosity of the resulting interface.

Author: eush77

README.md

@@ -76,11 +76,10 @@ filter(ast, (node) => node.type != 'leaf' || node.value % 2 == 0)
 
 ## API
 
-### `filter(ast, [opts], predicate, [context])`
+### `filter(ast, [opts], predicate)`
 
 - `ast` — [Unist] tree.
 - `predicate` — Function invoked with arguments `(node, index?, parent?)` or string (type test) or node (identity test) to test each node. See [unist-util-is] for details. In a function form, return `true` to keep the node, `false` otherwise.
-- `context` — Optional. Value to use as `this` when executing `predicate`.
 
 Executes `predicate` for each node in preorder tree traversal. Returns a new tree (or `null`) with nodes for which `predicate` returned `true`.
 

index.js

@@ -4,16 +4,15 @@ var flatmap = require('flatmap'),
     is = require('unist-util-is');
 
 
-module.exports = function (ast, opts, predicate, context) {
+module.exports = function (ast, opts, predicate) {
   if (arguments.length == 2) {
-    context = predicate;
     predicate = opts;
     opts = {};
   }
   opts.cascade = opts.cascade || opts.cascade === undefined;
 
   return (function preorder (node, index, parent) {
-    if (!is(predicate, node, index, parent, context)) {
+    if (!is(predicate, node, index, parent)) {
       return null;
     }
 

test/test.js

@@ -112,17 +112,6 @@ it('should call iterator with `index` and `parent` args', function (t) {
 });
 
 
-it('should call iterator in a context passed in as the last arg', function (t) {
-  var context = Object.create(null);
-
-  filter(u('root'), function () {
-    t.equal(this, context);
-  }, context);
-
-  t.end();
-});
-
-
 it('should support type and node tests', function (t) {
   var ast = u('node', [
     u('node', [