perf: improve evaluation speed of conditional queries

Use NodeJS' vm.Script class to cache the script that the context needs
to be evaluated against. This provides large speed improvements (~50%)
when a path contains conditional or JS logic.

src/jsonpath-browser.js

@@ -32,14 +32,24 @@ const moveToAnotherArray = function (source, target, conditionCb) {
     }
 };
 
-JSONPath.prototype.vm = {
+/**
+ * In-browser replacement for NodeJS' VM.Script.
+ */
+class Script {
     /**
      * @param {string} expr Expression to evaluate
+     */
+    constructor (expr) {
+        this.code = expr;
+    }
+
+    /**
      * @param {PlainObject} context Object whose items will be added
      *   to evaluation
      * @returns {EvaluatedResult} Result of evaluated code
      */
-    runInNewContext (expr, context) {
+    runInNewContext (context) {
+        let expr = this.code;
         const keys = Object.keys(context);
         const funcs = [];
         moveToAnotherArray(keys, funcs, (key) => {
@@ -81,6 +91,10 @@ JSONPath.prototype.vm = {
         // eslint-disable-next-line no-new-func
         return (new Function(...keys, code))(...values);
     }
+}
+
+JSONPath.prototype.vm = {
+    Script
 };
 
 export {JSONPath};

src/jsonpath.js

@@ -588,32 +588,34 @@ JSONPath.prototype._slice = function (
 JSONPath.prototype._eval = function (
     code, _v, _vname, path, parent, parentPropName
 ) {
-    if (code.includes('@parentProperty')) {
-        this.currSandbox._$_parentProperty = parentPropName;
-        code = code.replace(/@parentProperty/gu, '_$_parentProperty');
-    }
-    if (code.includes('@parent')) {
-        this.currSandbox._$_parent = parent;
-        code = code.replace(/@parent/gu, '_$_parent');
-    }
-    if (code.includes('@property')) {
-        this.currSandbox._$_property = _vname;
-        code = code.replace(/@property/gu, '_$_property');
-    }
-    if (code.includes('@path')) {
+    this.currSandbox._$_parentProperty = parentPropName;
+    this.currSandbox._$_parent = parent;
+    this.currSandbox._$_property = _vname;
+    this.currSandbox._$_root = this.json;
+    this.currSandbox._$_v = _v;
+
+    const containsPath = code.includes('@path');
+    if (containsPath) {
         this.currSandbox._$_path = JSONPath.toPathString(path.concat([_vname]));
-        code = code.replace(/@path/gu, '_$_path');
-    }
-    if (code.includes('@root')) {
-        this.currSandbox._$_root = this.json;
-        code = code.replace(/@root/gu, '_$_root');
     }
-    if ((/@([.\s)[])/u).test(code)) {
-        this.currSandbox._$_v = _v;
-        code = code.replace(/@([.\s)[])/gu, '_$_v$1');
+
+    const scriptCacheKey = 'script:' + code;
+    if (!JSONPath.cache[scriptCacheKey]) {
+        let script = code
+            .replace(/@parentProperty/gu, '_$_parentProperty')
+            .replace(/@parent/gu, '_$_parent')
+            .replace(/@property/gu, '_$_property')
+            .replace(/@root/gu, '_$_root')
+            .replace(/@([.\s)[])/gu, '_$_v$1');
+        if (containsPath) {
+            script = script.replace(/@path/gu, '_$_path');
+        }
+
+        JSONPath.cache[scriptCacheKey] = new this.vm.Script(script);
     }
+
     try {
-        return this.vm.runInNewContext(code, this.currSandbox);
+        return JSONPath.cache[scriptCacheKey].runInNewContext(this.currSandbox);
     } catch (e) {
         throw new Error('jsonPath: ' + e.message + ': ' + code);
     }

test/test.errors.js

@@ -20,7 +20,7 @@ checkBuiltInVMAndNodeVM(function (vmType, setBuiltInState) {
         it('should throw with a bad filter', () => {
             expect(() => {
                 jsonpath({json: {book: []}, path: '$..[?(@.category === category)]'});
-            }).to.throw(Error, 'jsonPath: category is not defined: _$_v.category === category');
+            }).to.throw(Error, 'jsonPath: category is not defined: @.category === category');
         });
 
         it('should throw with a bad result type', () => {