perf: improve parser performance

Author: anonrig

lib/parse.js

@@ -5,11 +5,13 @@
  * @param {string} input
  */
 function parse(input) {
-  let result = Object.create(null);
+  const result = Object.create(null);
 
-  let currentKey = "";
-  let currentValue = "";
-  let seenEqualOperator = false;
+  let key = "";
+  let value = "";
+  let separatorIndex = 0;
+  let equalityIndex = 0;
+  let shouldEncode = false;
 
   // Have a boundary of input.length + 1 to access last pair inside the loop.
   for (let i = 0; i < input.length + 1; i++) {
@@ -18,29 +20,44 @@ function parse(input) {
     // Handle '&' and end of line to pass the current values to result
     if (c === 38 || isNaN(c)) {
       // Disallow empty key values.
-      if (currentKey.length === 0) {
-        continue
-      } else if (typeof result[currentKey] === "undefined") {
-        result[currentKey] = currentValue;
-      } else if (Array.isArray(result[currentKey])) {
-        result[currentKey].push(currentValue);
-      } else {
-        result[currentKey] = [result[currentKey], currentValue];
+      if (equalityIndex - separatorIndex > 0 && i - equalityIndex + 1 > 0) {
+        key = input.slice(separatorIndex, equalityIndex);
+        value = input.slice(equalityIndex + 1, i);
+
+        // Optimization: Do not decode if it's not necessary.
+        if (shouldEncode) {
+          key = decodeURIComponent(key);
+          value = decodeURIComponent(value);
+        }
+
+        if (result[key] === undefined) {
+          result[key] = value;
+        } else {
+          const currentValue = result[key];
+
+          if (currentValue.pop) {
+            currentValue.push(value);
+          } else {
+            result[key] = [currentValue, value];
+          }
+        }
       }
 
       // Reset reading key value pairs
-      currentKey = "";
-      currentValue = "";
-      seenEqualOperator = false;
+      separatorIndex = i + 1;
+      equalityIndex = i + 1;
     }
     // Handle equal operator
     else if (c === 61) {
-      seenEqualOperator = true;
+      equalityIndex = i;
+    }
+    // Check '+', and replace it with empty space.
+    else if (c === 43) {
+      input[i] = " ";
     } else {
-      if (seenEqualOperator) {
-        currentValue += input[i];
-      } else {
-        currentKey += input[i];
+      // Check '%' character for encoding
+      if (c === 37) {
+        shouldEncode = true;
       }
     }
   }

test/basics.test.ts

@@ -1,25 +1,27 @@
 import qs from "../lib";
 import { test, assert } from "vitest";
-import vm from 'node:vm'
+import vm from "node:vm";
 
 const foreignObject = vm.runInNewContext('({"foo": ["bar", "baz"]})');
 const qsNoMungeTestCases = [
-  ['', {}],
-  ['foo=bar&foo=baz', { 'foo': ['bar', 'baz'] }],
-  ['foo=bar&foo=baz', foreignObject],
-  ['blah=burp', { 'blah': 'burp' }],
-  ['a=!-._~\'()*', { 'a': '!-._~\'()*' }],
-  ['a=abcdefghijklmnopqrstuvwxyz', { 'a': 'abcdefghijklmnopqrstuvwxyz' }],
-  ['a=ABCDEFGHIJKLMNOPQRSTUVWXYZ', { 'a': 'ABCDEFGHIJKLMNOPQRSTUVWXYZ' }],
-  ['a=0123456789', { 'a': '0123456789' }],
-  ['gragh=1&gragh=3&goo=2', { 'gragh': ['1', '3'], 'goo': '2' }],
-  ['frappucino=muffin&goat%5B%5D=scone&pond=moose',
-   { 'frappucino': 'muffin', 'goat[]': 'scone', 'pond': 'moose' }],
-  ['trololol=yes&lololo=no', { 'trololol': 'yes', 'lololo': 'no' }],
+  ["", {}],
+  ["foo=bar&foo=baz", { foo: ["bar", "baz"] }],
+  ["foo=bar&foo=baz", foreignObject],
+  ["blah=burp", { blah: "burp" }],
+  ["a=!-._~'()*", { a: "!-._~'()*" }],
+  ["a=abcdefghijklmnopqrstuvwxyz", { a: "abcdefghijklmnopqrstuvwxyz" }],
+  ["a=ABCDEFGHIJKLMNOPQRSTUVWXYZ", { a: "ABCDEFGHIJKLMNOPQRSTUVWXYZ" }],
+  ["a=0123456789", { a: "0123456789" }],
+  ["gragh=1&gragh=3&goo=2", { gragh: ["1", "3"], goo: "2" }],
+  [
+    "frappucino=muffin&goat%5B%5D=scone&pond=moose",
+    { frappucino: "muffin", "goat[]": "scone", pond: "moose" },
+  ],
+  ["trololol=yes&lololo=no", { trololol: "yes", lololo: "no" }],
 ];
 
 test("should parse the basics", () => {
   qsNoMungeTestCases.forEach((t) => {
-    assert.deepEqual(qs.parse(t[0]), t[1])
-  })
+    assert.deepEqual(qs.parse(t[0]), t[1]);
+  });
 });

test/benchmark.mjs

@@ -8,7 +8,7 @@ import queryString from "query-string";
 await benchmark(
   {
     URLStateMachine() {
-      return new URLStateMachine("hello=world&foo=bar", null, null, 115);
+      return new URLStateMachine("hello=world&foo=bar", undefined, null, 115);
     },
     qs() {
       return qs.parse("hello=world&foo=bar");