# path-expression-matcher Efficient path tracking and pattern matching for XML, JSON, YAML or any other parsers. ## 🎯 Purpose `path-expression-matcher` provides three core classes for tracking and matching paths: - **`Expression`**: Parses and stores pattern expressions (e.g., `"root.users.user[id]"`) - **`Matcher`**: Tracks current path during parsing and matches against expressions - **`MatcherView`**: A lightweight read-only view of a `Matcher`, safe to pass to callbacks Compatible with [fast-xml-parser](https://github.com/NaturalIntelligence/fast-xml-parser) and similar tools. ## 📦 Installation ```bash npm install path-expression-matcher ``` ## 🚀 Quick Start ```javascript import { Expression, Matcher } from 'path-expression-matcher'; // Create expression (parse once, reuse many times) const expr = new Expression("root.users.user"); // Create matcher (tracks current path) const matcher = new Matcher(); matcher.push("root"); matcher.push("users"); matcher.push("user", { id: "123" }); // Match current path against expression if (matcher.matches(expr)) { console.log("Match found!"); console.log("Current path:", matcher.toString()); // "root.users.user" } // Namespace support const nsExpr = new Expression("soap::Envelope.soap::Body..ns::UserId"); matcher.push("Envelope", null, "soap"); matcher.push("Body", null, "soap"); matcher.push("UserId", null, "ns"); console.log(matcher.toString()); // "soap:Envelope.soap:Body.ns:UserId" ``` ## 📖 Pattern Syntax ### Basic Paths ```javascript "root.users.user" // Exact path match "*.users.user" // Wildcard: any parent "root.*.user" // Wildcard: any middle "root.users.*" // Wildcard: any child ``` ### Deep Wildcard ```javascript "..user" // user anywhere in tree "root..user" // user anywhere under root "..users..user" // users somewhere, then user below it ``` ### Attribute Matching ```javascript "user[id]" // user with "id" attribute "user[type=admin]" // user with type="admin" (current node only) "root[lang]..user" // user under root that has "lang" attribute ``` ### Position Selectors ```javascript "user:first" // First user (counter=0) "user:nth(2)" // Third user (counter=2, zero-based) "user:odd" // Odd-numbered users (counter=1,3,5...) "user:even" // Even-numbered users (counter=0,2,4...) "root.users.user:first" // First user under users ``` **Note:** Position selectors use the **counter** (occurrence count of the tag name), not the position (child index). For example, in ``, the second `` has position=2 but counter=1. ### Namespaces ```javascript "ns::user" // user with namespace "ns" "soap::Envelope" // Envelope with namespace "soap" "ns::user[id]" // user with namespace "ns" and "id" attribute "ns::user:first" // First user with namespace "ns" "*::user" // user with any namespace "..ns::item" // item with namespace "ns" anywhere in tree "soap::Envelope.soap::Body" // Nested namespaced elements "ns::first" // Tag named "first" with namespace "ns" (NO ambiguity!) ``` **Namespace syntax:** - Use **double colon (::)** for namespace: `ns::tag` - Use **single colon (:)** for position: `tag:first` - Combined: `ns::tag:first` (namespace + tag + position) **Namespace matching rules:** - Pattern `ns::user` matches only nodes with namespace "ns" and tag "user" - Pattern `user` (no namespace) matches nodes with tag "user" regardless of namespace - Pattern `*::user` matches tag "user" with any namespace (wildcard namespace) - Namespaces are tracked separately for counter/position (e.g., `ns1::item` and `ns2::item` have independent counters) ### Wildcard Differences **Single wildcard (`*`)** - Matches exactly ONE level: - `"*.fix1"` matches `root.fix1` (2 levels) ✅ - `"*.fix1"` does NOT match `root.another.fix1` (3 levels) ❌ - Path depth MUST equal pattern depth **Deep wildcard (`..`)** - Matches ZERO or MORE levels: - `"..fix1"` matches `root.fix1` ✅ - `"..fix1"` matches `root.another.fix1` ✅ - `"..fix1"` matches `a.b.c.d.fix1` ✅ - Works at any depth ### Combined Patterns ```javascript "..user[id]:first" // First user with id, anywhere "root..user[type=admin]" // Admin user under root "ns::user[id]:first" // First namespaced user with id "soap::Envelope..ns::UserId" // UserId with namespace ns under SOAP envelope ``` ## 🔧 API Reference ### Expression #### Constructor ```javascript new Expression(pattern, options = {}, data) ``` **Parameters:** - `pattern` (string): Pattern to parse - `options.separator` (string): Path separator (default: `'.'`) **Example:** ```javascript const expr1 = new Expression("root.users.user"); const expr2 = new Expression("root/users/user", { separator: '/' }); const expr3 = new Expression("root/users/user", { separator: '/' }, { extra: "data"}); console.log(expr3.data) // { extra: "data" } ``` #### Methods - `hasDeepWildcard()` → boolean - `hasAttributeCondition()` → boolean - `hasPositionSelector()` → boolean - `toString()` → string ### Matcher #### Constructor ```javascript new Matcher(options) ``` **Parameters:** - `options.separator` (string): Default path separator (default: `'.'`) #### Path Tracking Methods ##### `push(tagName, attrValues, namespace)` Add a tag to the current path. Position and counter are automatically calculated. **Parameters:** - `tagName` (string): Tag name - `attrValues` (object, optional): Attribute key-value pairs (current node only) - `namespace` (string, optional): Namespace for the tag **Example:** ```javascript matcher.push("user", { id: "123", type: "admin" }); matcher.push("item"); // No attributes matcher.push("Envelope", null, "soap"); // With namespace matcher.push("Body", { version: "1.1" }, "soap"); // With both ``` **Position vs Counter:** - **Position**: The child index in the parent (0, 1, 2, 3...) - **Counter**: How many times this tag name appeared at this level (0, 1, 2...) Example: ```xml ``` ##### `pop()` Remove the last tag from the path. ```javascript matcher.pop(); ``` ##### `updateCurrent(attrValues)` Update current node's attributes (useful when attributes are parsed after push). ```javascript matcher.push("user"); // Don't know values yet // ... parse attributes ... matcher.updateCurrent({ id: "123" }); ``` ##### `reset()` Clear the entire path. ```javascript matcher.reset(); ``` #### Query Methods ##### `matches(expression)` Check if current path matches an Expression. ```javascript const expr = new Expression("root.users.user"); if (matcher.matches(expr)) { // Current path matches } ``` #### `matchesAny(exprSet)` → `boolean` Please check `ExpressionSet` class for more details. ```javascript const matcher = new Matcher(); const exprSet = new ExpressionSet(); exprSet.add(new Expression("root.users.user")); exprSet.add(new Expression("root.config.*")); exprSet.seal(); if (matcher.matchesAny(exprSet)) { // Current path matches any expression in the set } ``` ##### `getCurrentTag()` Get current tag name. ```javascript const tag = matcher.getCurrentTag(); // "user" ``` ##### `getCurrentNamespace()` Get current namespace. ```javascript const ns = matcher.getCurrentNamespace(); // "soap" or undefined ``` ##### `getAttrValue(attrName)` Get attribute value of current node. ```javascript const id = matcher.getAttrValue("id"); // "123" ``` ##### `hasAttr(attrName)` Check if current node has an attribute. ```javascript if (matcher.hasAttr("id")) { // Current node has "id" attribute } ``` ##### `getPosition()` Get sibling position of current node (child index in parent). ```javascript const position = matcher.getPosition(); // 0, 1, 2, ... ``` ##### `getCounter()` Get repeat counter of current node (occurrence count of this tag name). ```javascript const counter = matcher.getCounter(); // 0, 1, 2, ... ``` ##### `getIndex()` (deprecated) Alias for `getPosition()`. Use `getPosition()` or `getCounter()` instead for clarity. ```javascript const index = matcher.getIndex(); // Same as getPosition() ``` ##### `getDepth()` Get current path depth. ```javascript const depth = matcher.getDepth(); // 3 for "root.users.user" ``` ##### `toString(separator?, includeNamespace?)` Get path as string. **Parameters:** - `separator` (string, optional): Path separator (uses default if not provided) - `includeNamespace` (boolean, optional): Whether to include namespaces (default: true) ```javascript const path = matcher.toString(); // "root.ns:user.item" const path2 = matcher.toString('/'); // "root/ns:user/item" const path3 = matcher.toString('.', false); // "root.user.item" (no namespaces) ``` ##### `toArray()` Get path as array. ```javascript const arr = matcher.toArray(); // ["root", "users", "user"] ``` #### State Management ##### `snapshot()` Create a snapshot of current state. ```javascript const snapshot = matcher.snapshot(); ``` ##### `restore(snapshot)` Restore from a snapshot. ```javascript matcher.restore(snapshot); ``` #### Read-Only Access ##### `readOnly()` Returns a **`MatcherView`** — a lightweight, live read-only view of the matcher. All query and inspection methods work normally and always reflect the current state of the underlying matcher. Mutation methods (`push`, `pop`, `reset`, `updateCurrent`, `restore`) simply don't exist on `MatcherView`, so misuse is caught at **compile time** by TypeScript rather than at runtime. The **same instance** is returned on every call — no allocation occurs per invocation. This is the recommended way to share the matcher with callbacks, plugins, or any external code that only needs to inspect the current path. ```javascript const view = matcher.readOnly(); // Same reference every time — safe to cache view === matcher.readOnly(); // true ``` **What works on the view:** ```javascript view.matches(expr) // ✓ pattern matching view.getCurrentTag() // ✓ current tag name view.getCurrentNamespace() // ✓ current namespace view.getAttrValue("id") // ✓ attribute value view.hasAttr("id") // ✓ attribute presence check view.getPosition() // ✓ sibling position view.getCounter() // ✓ occurrence counter view.getDepth() // ✓ path depth view.toString() // ✓ path as string view.toArray() // ✓ path as array ``` **What doesn't exist (compile-time error in TypeScript):** ```javascript view.push("child", {}) // ✗ Property 'push' does not exist on type 'MatcherView' view.pop() // ✗ Property 'pop' does not exist on type 'MatcherView' view.reset() // ✗ Property 'reset' does not exist on type 'MatcherView' view.updateCurrent({}) // ✗ Property 'updateCurrent' does not exist on type 'MatcherView' view.restore(snapshot) // ✗ Property 'restore' does not exist on type 'MatcherView' ``` **The view is live** — it always reflects the current state of the underlying matcher. ```javascript const matcher = new Matcher(); const view = matcher.readOnly(); matcher.push("root"); view.getDepth(); // 1 — immediately reflects the push matcher.push("users"); view.getDepth(); // 2 — still live ``` ## 💡 Usage Examples ### Example 1: XML Parser with stopNodes ```javascript import { XMLParser } from 'fast-xml-parser'; import { Expression, Matcher } from 'path-expression-matcher'; class MyParser { constructor() { this.matcher = new Matcher(); // Pre-compile stop node patterns this.stopNodeExpressions = [ new Expression("html.body.script"), new Expression("html.body.style"), new Expression("..svg"), ]; } parseTag(tagName, attrs) { this.matcher.push(tagName, attrs); // Check if this is a stop node for (const expr of this.stopNodeExpressions) { if (this.matcher.matches(expr)) { // Don't parse children, read as raw text return this.readRawContent(); } } // Continue normal parsing this.parseChildren(); this.matcher.pop(); } } ``` ### Example 2: Conditional Processing ```javascript const matcher = new Matcher(); const userExpr = new Expression("..user[type=admin]"); const firstItemExpr = new Expression("..item:first"); function processTag(tagName, value, attrs) { matcher.push(tagName, attrs); if (matcher.matches(userExpr)) { value = enhanceAdminUser(value); } if (matcher.matches(firstItemExpr)) { value = markAsFirst(value); } matcher.pop(); return value; } ``` ### Example 3: Path-based Filtering ```javascript const patterns = [ new Expression("data.users.user"), new Expression("data.posts.post"), new Expression("..comment[approved=true]"), ]; function shouldInclude(matcher) { return patterns.some(expr => matcher.matches(expr)); } ``` ### Example 4: Custom Separator ```javascript const matcher = new Matcher({ separator: '/' }); const expr = new Expression("root/config/database", { separator: '/' }); matcher.push("root"); matcher.push("config"); matcher.push("database"); console.log(matcher.toString()); // "root/config/database" console.log(matcher.matches(expr)); // true ``` ### Example 5: Attribute Checking ```javascript const matcher = new Matcher(); matcher.push("root"); matcher.push("user", { id: "123", type: "admin", status: "active" }); // Check attribute existence (current node only) console.log(matcher.hasAttr("id")); // true console.log(matcher.hasAttr("email")); // false // Get attribute value (current node only) console.log(matcher.getAttrValue("type")); // "admin" // Match by attribute const expr1 = new Expression("user[id]"); console.log(matcher.matches(expr1)); // true const expr2 = new Expression("user[type=admin]"); console.log(matcher.matches(expr2)); // true ``` ### Example 6: Position vs Counter ```javascript const matcher = new Matcher(); matcher.push("root"); // Mixed tags at same level matcher.push("item"); // position=0, counter=0 (first item) matcher.pop(); matcher.push("div"); // position=1, counter=0 (first div) matcher.pop(); matcher.push("item"); // position=2, counter=1 (second item) console.log(matcher.getPosition()); // 2 (third child overall) console.log(matcher.getCounter()); // 1 (second "item" specifically) // :first uses counter, not position const expr = new Expression("root.item:first"); console.log(matcher.matches(expr)); // false (counter=1, not 0) ``` ### Example 8: Passing a Read-Only View to External Consumers When passing the matcher into callbacks, plugins, or other code you don't control, use `readOnly()` to get a `MatcherView` — it can inspect but never mutate parser state. ```javascript import { Expression, Matcher } from 'path-expression-matcher'; const matcher = new Matcher(); const adminExpr = new Expression("..user[type=admin]"); function parseTag(tagName, attrs, onTag) { matcher.push(tagName, attrs); // Pass MatcherView — consumer can inspect but not mutate onTag(matcher.readOnly()); matcher.pop(); } // Safe consumer — can only read function myPlugin(view) { if (view.matches(adminExpr)) { console.log("Admin at path:", view.toString()); console.log("Depth:", view.getDepth()); console.log("ID:", view.getAttrValue("id")); } } // view.push(...) or view.reset() don't exist on MatcherView — // TypeScript catches misuse at compile time. parseTag("user", { id: "1", type: "admin" }, myPlugin); ``` ```javascript const matcher = new Matcher(); const soapExpr = new Expression("soap::Envelope.soap::Body..ns::UserId"); // Parse SOAP document matcher.push("Envelope", { xmlns: "..." }, "soap"); matcher.push("Body", null, "soap"); matcher.push("GetUserRequest", null, "ns"); matcher.push("UserId", null, "ns"); // Match namespaced pattern if (matcher.matches(soapExpr)) { console.log("Found UserId in SOAP body"); console.log(matcher.toString()); // "soap:Envelope.soap:Body.ns:GetUserRequest.ns:UserId" } // Namespace-specific counters matcher.reset(); matcher.push("root"); matcher.push("item", null, "ns1"); // ns1::item counter=0 matcher.pop(); matcher.push("item", null, "ns2"); // ns2::item counter=0 (different namespace) matcher.pop(); matcher.push("item", null, "ns1"); // ns1::item counter=1 const firstNs1Item = new Expression("root.ns1::item:first"); console.log(matcher.matches(firstNs1Item)); // false (counter=1) const secondNs1Item = new Expression("root.ns1::item:nth(1)"); console.log(matcher.matches(secondNs1Item)); // true // NO AMBIGUITY: Tags named after position keywords matcher.reset(); matcher.push("root"); matcher.push("first", null, "ns"); // Tag named "first" with namespace const expr = new Expression("root.ns::first"); console.log(matcher.matches(expr)); // true - matches namespace "ns", tag "first" ``` ## 🏗️ Architecture ### Data Storage Strategy **Ancestor nodes:** Store only tag name, position, and counter (minimal memory) **Current node:** Store tag name, position, counter, and attribute values This design minimizes memory usage: - No attribute names stored (derived from values object when needed) - Attribute values only for current node, not ancestors - Attribute checking for ancestors is not supported (acceptable trade-off) - For 1M nodes with 3 attributes each, saves ~50MB vs storing attribute names ### Matching Strategy Matching is performed **bottom-to-top** (from current node toward root): 1. Start at current node 2. Match segments from pattern end to start 3. Attribute checking only works for current node (ancestors have no attribute data) 4. Position selectors use **counter** (occurrence count), not position (child index) ### Performance - **Expression parsing:** One-time cost when Expression is created - **Expression analysis:** Cached (hasDeepWildcard, hasAttributeCondition, hasPositionSelector) - **Path tracking:** O(1) for push/pop operations - **Pattern matching:** O(n*m) where n = path depth, m = pattern segments - **Memory per ancestor node:** ~40-60 bytes (tag, position, counter only) - **Memory per current node:** ~80-120 bytes (adds attribute values) ## 🎓 Design Patterns ### Pre-compile Patterns (Recommended) ```javascript // ✅ GOOD: Parse once, reuse many times const expr = new Expression("..user[id]"); for (let i = 0; i < 1000; i++) { if (matcher.matches(expr)) { // ... } } ``` ```javascript // ❌ BAD: Parse on every iteration for (let i = 0; i < 1000; i++) { if (matcher.matches(new Expression("..user[id]"))) { // ... } } ``` ### Batch Pattern Checking with ExpressionSet (Recommended) For checking multiple patterns on every tag, use `ExpressionSet` instead of a manual loop. It pre-indexes expressions at build time so each call to `matchesAny()` does an O(1) bucket lookup rather than a full O(N) scan: ```javascript import { Expression, ExpressionSet, Matcher } from 'path-expression-matcher'; // Build once at config/startup time const stopNodes = new ExpressionSet(); stopNodes .add(new Expression('root.users.user')) .add(new Expression('root.config.*')) .add(new Expression('..script')) .seal(); // prevent accidental mutation during parsing // Per-tag — hot path if (stopNodes.matchesAny(matcher)) { // handle stop node } ``` This replaces the manual loop pattern: ```javascript // ❌ Before — O(N) per tag function isStopNode(expressions, matcher) { for (let i = 0; i < expressions.length; i++) { if (matcher.matches(expressions[i])) return true; } return false; } // ✅ After — O(1) lookup per tag const stopNodes = new ExpressionSet(); stopNodes.addAll(expressions); stopNodes.matchesAny(matcher); //or matcher.matchesAny(stopNodes) ``` --- ## 📦 ExpressionSet API `ExpressionSet` is an indexed collection of `Expression` objects designed for efficient bulk matching. Build it once from your config, then call `matchesAny()` on every tag. ### Constructor ```javascript const set = new ExpressionSet(); ``` ### `add(expression)` → `this` Add a single `Expression`. Duplicate patterns (same pattern string) are silently ignored. Returns `this` for chaining. Throws `TypeError` if the set is sealed. ```javascript set.add(new Expression('root.users.user')); set.add(new Expression('..script')); ``` ### `addAll(expressions)` → `this` Add an array of `Expression` objects at once. Returns `this` for chaining. ```javascript set.addAll(config.stopNodes.map(p => new Expression(p))); ``` ### `has(expression)` → `boolean` Check whether an expression with the same pattern is already present. ```javascript set.has(new Expression('root.users.user')); // true / false ``` ### `seal()` → `this` Prevent further additions. Any subsequent call to `add()` or `addAll()` throws a `TypeError`. Useful to guard against accidental mutation once parsing has started. ```javascript const stopNodes = new ExpressionSet(); stopNodes.addAll(patterns).seal(); stopNodes.add(new Expression('root.extra')); // ❌ TypeError: ExpressionSet is sealed ``` ### `size` → `number` Number of distinct expressions in the set. ```javascript set.size; // 3 ``` ### `isSealed` → `boolean` Whether `seal()` has been called. ### `matchesAny(matcher)` → `boolean` Returns `true` if the matcher's current path matches **any** expression in the set. Accepts both a `Matcher` instance and a `MatcherView`. ```javascript if (stopNodes.matchesAny(matcher)) { /* ... */ } if (stopNodes.matchesAny(matcher.readOnly())) { /* ... */ } // also works ``` **How indexing works:** expressions are bucketed at `add()` time, not at match time. | Expression type | Bucket | Lookup cost | |---|---|---| | Fixed path, concrete tag (`root.users.user`) | `depth:tag` map | O(1) | | Fixed path, wildcard tag (`root.config.*`) | `depth` map | O(1) | | Deep wildcard (`..script`) | flat list | O(D) — always scanned | In practice, deep-wildcard expressions are rare in configs, so the list stays small. ### `findMatch(matcher)` → `Expression` Returns the Expression instance that matched the current path. Accepts both a `Matcher` instance and a `MatcherView`. ```javascript const node = stopNodes.findMatch(matcher); ``` ### Example 7: ExpressionSet in a real parser loop ```javascript import { XMLParser } from 'fast-xml-parser'; import { Expression, ExpressionSet, Matcher } from 'path-expression-matcher'; // Config-time setup const stopNodes = new ExpressionSet(); stopNodes .addAll(['script', 'style'].map(t => new Expression(`..${t}`))) .seal(); const matcher = new Matcher(); const parser = new XMLParser({ onOpenTag(tagName, attrs) { matcher.push(tagName, attrs); if (stopNodes.matchesAny(matcher)) { // treat as stop node } }, onCloseTag() { matcher.pop(); }, }); ``` ## 🔗 Integration with fast-xml-parser **Basic integration:** ```javascript import { XMLParser } from 'fast-xml-parser'; import { Expression, Matcher } from 'path-expression-matcher'; const parser = new XMLParser({ // Custom options using path-expression-matcher stopNodes: ["script", "style"].map(tag => new Expression(`..${tag}`)), tagValueProcessor: (tagName, value, jPath, hasAttrs, isLeaf, matcher) => { // matcher is available in callbacks if (matcher.matches(new Expression("..user[type=admin]"))) { return enhanceValue(value); } return value; } }); ``` ## 📄 License MIT ## 🤝 Contributing Issues and PRs welcome! This package is designed to be used by XML/JSON parsers like fast-xml-parser. But can be used with any formar parser.

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zip	src/	4096	---	2026-06-06 17:49:09
-	LICENSE	1056	%	2026-06-06 17:49:08
-	README.md	24024	md	2026-06-06 17:49:09
-	package.json	1840	json	2026-06-06 17:49:09

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