Refactor: Modularize parse.js and add unit tests

.eslintrc.json

@@ -0,0 +1,19 @@
+{
+  "extends": "eslint:recommended",
+  "env": {
+    "browser": false,
+    "node": true,
+    "es2020": true,
+    "mocha": true
+  },
+  "parserOptions": {
+    "ecmaVersion": 2022,
+    "sourceType": "module"
+  },
+  "rules": {
+    "no-unused-vars": ["warn", { "argsIgnorePattern": "^_" }],
+    "no-prototype-builtins": "off",
+    "no-undef": "warn",
+    "no-constant-condition": ["error", { "checkLoops": false }]
+  }
+}

src/expression/error.js

@@ -0,0 +1,40 @@
+/**
+ * Shortcut for getting the current col value (one based)
+ * Returns the column (position) where the last state.token starts
+ * @param {Object} state
+ * @return {number}
+ * @private
+ */
+export function col (state) {
+  return state.index - state.token.length + 1
+}
+
+/**
+ * Create a syntax error with the message:
+ *     'Syntax error in part "<part>" (char <char>)'
+ * @param {Object} state
+ * @param {string} message
+ * @return {SyntaxError} instantiated error
+ * @private
+ */
+export function createSyntaxError (state, message) {
+  const c = col(state)
+  const error = new SyntaxError(message + ' (char ' + c + ')')
+  error.char = c
+  return error
+}
+
+/**
+ * Create an error with the message:
+ *     '<message> (char <char>)'
+ * @param {Object} state
+ * @param {string} message
+ * @return {Error} instantiated error
+ * @private
+ */
+export function createError (state, message) {
+  const c = col(state)
+  const error = new Error(message + ' (char ' + c + ')') // Changed to regular Error as per original type, can be SyntaxError if preferred
+  error.char = c
+  return error
+}