js: Convert _.map(a, …) to a.map(…).

And convert the corresponding function expressions to arrow style
while we’re here.

import * as babelParser from "recast/parsers/babel";
import * as recast from "recast";
import * as tsParser from "recast/parsers/typescript";
import { builders as b, namedTypes as n } from "ast-types";
import K from "ast-types/gen/kinds";
import fs from "fs";
import path from "path";
import process from "process";

const checkExpression = (node: n.Node): node is K.ExpressionKind =>
  n.Expression.check(node);

for (const file of process.argv.slice(2)) {
  console.log("Parsing", file);
  const ast = recast.parse(fs.readFileSync(file, { encoding: "utf8" }), {
    parser: path.extname(file) === ".ts" ? tsParser : babelParser,
  });
  let changed = false;

  recast.visit(ast, {
    visitCallExpression(path) {
      const { callee, arguments: args } = path.node;
      if (
        n.MemberExpression.check(callee) &&
        !callee.computed &&
        n.Identifier.check(callee.object) &&
        callee.object.name === "_" &&
        n.Identifier.check(callee.property) &&
        callee.property.name === "map" &&
        args.length === 2 &&
        checkExpression(args[0]) &&
        checkExpression(args[1])
      ) {
        const [arr, fn] = args;
        path.replace(
          b.callExpression(b.memberExpression(arr, b.identifier("map")), [
            n.FunctionExpression.check(fn) ||
            n.ArrowFunctionExpression.check(fn)
              ? b.arrowFunctionExpression(
                  fn.params,
                  n.BlockStatement.check(fn.body) &&
                    fn.body.body.length === 1 &&
                    n.ReturnStatement.check(fn.body.body[0])
                    ? fn.body.body[0].argument || b.identifier("undefined")
                    : fn.body
                )
              : fn,
          ])
        );
        changed = true;
      }
      this.traverse(path);
    },
  });

  if (changed) {
    console.log("Writing", file);
    fs.writeFileSync(file, recast.print(ast).code, { encoding: "utf8" });
  }
}

Signed-off-by: Anders Kaseorg <anders@zulipchat.com>

static/js/message_fetch.js

@@ -26,7 +26,7 @@ function process_result(data, opts) {
     }
 
     _.each(messages, message_store.set_message_booleans);
-    messages = _.map(messages, message_store.add_message_metadata);
+    messages = messages.map(message_store.add_message_metadata);
 
     // In case any of the newly fetched messages are new, add them to
     // our unread data structures.  It's important that this run even
@@ -118,7 +118,7 @@ function handle_operators_supporting_id_based_api(data) {
     }
 
     data.narrow = JSON.parse(data.narrow);
-    data.narrow = _.map(data.narrow, function (filter) {
+    data.narrow = data.narrow.map(filter => {
         if (operators_supporting_ids.includes(filter.operator)) {
             filter.operand = people.emails_strings_to_user_ids_array(filter.operand);
         }