Add node querystring polyfill (#4370)

std/node/README.md

@@ -27,7 +27,7 @@ deno standard library as it's a compatiblity module.
 - [x] path
 - [ ] perf_hooks
 - [x] process _partly_
-- [ ] querystring
+- [x] querystring
 - [ ] readline
 - [ ] repl
 - [ ] stream

std/node/module.ts

@@ -27,6 +27,7 @@ import * as nodePath from "./path.ts";
 import * as nodeTimers from "./timers.ts";
 import * as nodeOs from "./os.ts";
 import * as nodeEvents from "./events.ts";
+import * as nodeQueryString from "./querystring.ts";
 
 import * as path from "../path/mod.ts";
 import { assert } from "../testing/asserts.ts";
@@ -593,6 +594,10 @@ nativeModulePolyfill.set("os", createNativeModule("os", nodeOs));
 nativeModulePolyfill.set("path", createNativeModule("path", nodePath));
 nativeModulePolyfill.set("timers", createNativeModule("timers", nodeTimers));
 nativeModulePolyfill.set("util", createNativeModule("util", nodeUtil));
+nativeModulePolyfill.set(
+  "querystring",
+  createNativeModule("querystring", nodeQueryString)
+);
 
 function loadNativeModule(
   _filename: string,

std/node/querystring.ts

@@ -0,0 +1,70 @@
+interface ParseOptions {
+  decodeURIComponent?: (string: string) => string;
+  maxKeys?: number;
+}
+
+export function parse(
+  str: string,
+  sep = "&",
+  eq = "=",
+  { decodeURIComponent = unescape, maxKeys = 1000 }: ParseOptions = {}
+): { [key: string]: string[] | string } {
+  const entries = str
+    .split(sep)
+    .map(entry => entry.split(eq).map(decodeURIComponent));
+  const final: { [key: string]: string[] | string } = {};
+
+  let i = 0;
+  while (true) {
+    if ((Object.keys(final).length === maxKeys && !!maxKeys) || !entries[i]) {
+      break;
+    }
+
+    const [key, val] = entries[i];
+    if (final[key]) {
+      if (Array.isArray(final[key])) {
+        (final[key] as string[]).push(val);
+      } else {
+        final[key] = [final[key] as string, val];
+      }
+    } else {
+      final[key] = val;
+    }
+
+    i++;
+  }
+
+  return final;
+}
+
+interface StringifyOptions {
+  encodeURIComponent?: (string: string) => string;
+}
+
+export function stringify(
+  obj: object,
+  sep = "&",
+  eq = "=",
+  { encodeURIComponent = escape }: StringifyOptions = {}
+): string {
+  const final = [];
+
+  for (const entry of Object.entries(obj)) {
+    if (Array.isArray(entry[1])) {
+      for (const val of entry[1]) {
+        final.push(encodeURIComponent(entry[0]) + eq + encodeURIComponent(val));
+      }
+    } else if (typeof entry[1] !== "object" && entry[1] !== undefined) {
+      final.push(entry.map(encodeURIComponent).join(eq));
+    } else {
+      final.push(encodeURIComponent(entry[0]) + eq);
+    }
+  }
+
+  return final.join(sep);
+}
+
+export const decode = parse;
+export const encode = stringify;
+export const unescape = decodeURIComponent;
+export const escape = encodeURIComponent;

std/node/querystring_test.ts

@@ -0,0 +1,30 @@
+const { test } = Deno;
+import { assertEquals } from "../testing/asserts.ts";
+import { stringify, parse } from "./querystring.ts";
+
+test({
+  name: "stringify",
+  fn() {
+    assertEquals(
+      stringify({
+        a: "hello",
+        b: 5,
+        c: true,
+        d: ["foo", "bar"]
+      }),
+      "a=hello&b=5&c=true&d=foo&d=bar"
+    );
+  }
+});
+
+test({
+  name: "parse",
+  fn() {
+    assertEquals(parse("a=hello&b=5&c=true&d=foo&d=bar"), {
+      a: "hello",
+      b: "5",
+      c: "true",
+      d: ["foo", "bar"]
+    });
+  }
+});