Improve performance by reducing array slices and RegExp recreation

src/EventEmitter.js

@@ -1,12 +1,21 @@
 class EventEmitter {
   constructor() {
+    // This is an Object containing Maps:
+    //
+    // { [event: string]: Map<listener: function, numTimesAdded: number> }
+    //
+    // We use a Map for O(1) insertion/deletion and because it can have functions as keys.
+    //
+    // We keep track of numTimesAdded (the number of times it was added) because if you attach the same listener twice,
+    // we should actually call it twice for each emitted event.
     this.observers = {};
   }
 
   on(events, listener) {
     events.split(' ').forEach((event) => {
-      this.observers[event] = this.observers[event] || [];
-      this.observers[event].push(listener);
+      if (!this.observers[event]) this.observers[event] = new Map();
+      const numListeners = this.observers[event].get(listener) || 0;
+      this.observers[event].set(listener, numListeners + 1);
     });
     return this;
   }
@@ -18,21 +27,25 @@ class EventEmitter {
       return;
     }
 
-    this.observers[event] = this.observers[event].filter((l) => l !== listener);
+    this.observers[event].delete(listener);
   }
 
   emit(event, ...args) {
     if (this.observers[event]) {
-      const cloned = [].concat(this.observers[event]);
-      cloned.forEach((observer) => {
-        observer(...args);
+      const cloned = Array.from(this.observers[event].entries());
+      cloned.forEach(([observer, numTimesAdded]) => {
+        for (let i = 0; i < numTimesAdded; i++) {
+          observer(...args);
+        }
       });
     }
 
     if (this.observers['*']) {
-      const cloned = [].concat(this.observers['*']);
-      cloned.forEach((observer) => {
-        observer.apply(observer, [event, ...args]);
+      const cloned = Array.from(this.observers['*'].entries());
+      cloned.forEach(([observer, numTimesAdded]) => {
+        for (let i = 0; i < numTimesAdded; i++) {
+          observer.apply(observer, [event, ...args]);
+        }
       });
     }
   }

src/Interpolator.js

@@ -70,15 +70,23 @@ class Interpolator {
   }
 
   resetRegExp() {
-    // the regexp
-    const regexpStr = `${this.prefix}(.+?)${this.suffix}`;
-    this.regexp = new RegExp(regexpStr, 'g');
-
-    const regexpUnescapeStr = `${this.prefix}${this.unescapePrefix}(.+?)${this.unescapeSuffix}${this.suffix}`;
-    this.regexpUnescape = new RegExp(regexpUnescapeStr, 'g');
+    const getOrResetRegExp = (existingRegExp, pattern) => {
+      if (existingRegExp && existingRegExp.source === pattern) {
+        existingRegExp.lastIndex = 0;
+        return existingRegExp;
+      }
+      return new RegExp(pattern, 'g');
+    };
 
-    const nestingRegexpStr = `${this.nestingPrefix}(.+?)${this.nestingSuffix}`;
-    this.nestingRegexp = new RegExp(nestingRegexpStr, 'g');
+    this.regexp = getOrResetRegExp(this.regexp, `${this.prefix}(.+?)${this.suffix}`);
+    this.regexpUnescape = getOrResetRegExp(
+      this.regexpUnescape,
+      `${this.prefix}${this.unescapePrefix}(.+?)${this.unescapeSuffix}${this.suffix}`,
+    );
+    this.nestingRegexp = getOrResetRegExp(
+      this.nestingRegexp,
+      `${this.nestingPrefix}(.+?)${this.nestingSuffix}`,
+    );
   }
 
   interpolate(str, data, lng, options) {

src/ResourceStore.js

@@ -37,13 +37,20 @@ class ResourceStore extends EventEmitter {
         ? options.ignoreJSONStructure
         : this.options.ignoreJSONStructure;
 
-    let path = [lng, ns];
-    if (key && typeof key !== 'string') path = path.concat(key);
-    if (key && typeof key === 'string')
-      path = path.concat(keySeparator ? key.split(keySeparator) : key);
-
+    let path;
     if (lng.indexOf('.') > -1) {
       path = lng.split('.');
+    } else {
+      path = [lng, ns];
+      if (key) {
+        if (Array.isArray(key)) {
+          path.push(...key);
+        } else if (typeof key === 'string' && keySeparator) {
+          path.push(...key.split(keySeparator));
+        } else {
+          path.push(key);
+        }
+      }
     }
 
     const result = utils.getPath(this.data, path);

src/utils.js

@@ -26,33 +26,40 @@ export function copy(a, s, t) {
   });
 }
 
+// We extract out the RegExp definition to improve performance with React Native Android, which has poor RegExp
+// initialization performance
+const lastOfPathSeparatorRegExp = /###/g;
+
 function getLastOfPath(object, path, Empty) {
   function cleanKey(key) {
-    return key && key.indexOf('###') > -1 ? key.replace(/###/g, '.') : key;
+    return key && key.indexOf('###') > -1 ? key.replace(lastOfPathSeparatorRegExp, '.') : key;
   }
 
   function canNotTraverseDeeper() {
     return !object || typeof object === 'string';
   }
 
-  const stack = typeof path !== 'string' ? [].concat(path) : path.split('.');
-  while (stack.length > 1) {
+  const stack = typeof path !== 'string' ? path : path.split('.');
+  let stackIndex = 0;
+  // iterate through the stack, but leave the last item
+  while (stackIndex < stack.length - 1) {
     if (canNotTraverseDeeper()) return {};
 
-    const key = cleanKey(stack.shift());
+    const key = cleanKey(stack[stackIndex]);
     if (!object[key] && Empty) object[key] = new Empty();
     // prevent prototype pollution
     if (Object.prototype.hasOwnProperty.call(object, key)) {
       object = object[key];
     } else {
       object = {};
     }
+    ++stackIndex;
   }
 
   if (canNotTraverseDeeper()) return {};
   return {
     obj: object,
-    k: cleanKey(stack.shift()),
+    k: cleanKey(stack[stackIndex]),
   };
 }
 
@@ -134,15 +141,50 @@ export function escape(data) {
   return data;
 }
 
+/**
+ * This is a reusable regular expression cache class. Given a certain maximum number of regular expressions we're
+ * allowed to store in the cache, it provides a way to avoid recreating regular expression objects over and over.
+ * When it needs to evict something, it evicts the oldest one.
+ */
+class RegExpCache {
+  constructor(capacity) {
+    this.capacity = capacity;
+    this.regExpMap = new Map();
+    // Since our capacity tends to be fairly small, `.shift()` will be fairly quick despite being O(n). We just use a
+    // normal array to keep it simple.
+    this.regExpQueue = [];
+  }
+
+  getRegExp(pattern) {
+    const regExpFromCache = this.regExpMap.get(pattern);
+    if (regExpFromCache !== undefined) {
+      return regExpFromCache;
+    }
+    const regExpNew = new RegExp(pattern);
+    if (this.regExpQueue.length === this.capacity) {
+      this.regExpMap.delete(this.regExpQueue.shift());
+    }
+    this.regExpMap.set(pattern, regExpNew);
+    this.regExpQueue.push(pattern);
+    return regExpNew;
+  }
+}
+
 const chars = [' ', ',', '?', '!', ';'];
+// We cache RegExps to improve performance with React Native Android, which has poor RegExp initialization performance.
+// Capacity of 20 should be plenty, as nsSeparator/keySeparator don't tend to vary much across calls.
+const looksLikeObjectPathRegExpCache = new RegExpCache(20);
+
 export function looksLikeObjectPath(key, nsSeparator, keySeparator) {
   nsSeparator = nsSeparator || '';
   keySeparator = keySeparator || '';
   const possibleChars = chars.filter(
     (c) => nsSeparator.indexOf(c) < 0 && keySeparator.indexOf(c) < 0,
   );
   if (possibleChars.length === 0) return true;
-  const r = new RegExp(`(${possibleChars.map((c) => (c === '?' ? '\\?' : c)).join('|')})`);
+  const r = looksLikeObjectPathRegExpCache.getRegExp(
+    `(${possibleChars.map((c) => (c === '?' ? '\\?' : c)).join('|')})`,
+  );
   let matched = !r.test(key);
   if (!matched) {
     const ki = key.indexOf(keySeparator);
@@ -153,36 +195,39 @@ export function looksLikeObjectPath(key, nsSeparator, keySeparator) {
   return matched;
 }
 
+/**
+ * Given
+ *
+ * 1. a top level object obj, and
+ * 2. a path to a deeply nested string or object within it
+ *
+ * Find and return that deeply nested string or object. The caveat is that the keys of objects within the nesting chain
+ * may contain period characters. Therefore, we need to DFS and explore all possible keys at each step until we find the
+ * deeply nested string or object.
+ */
 export function deepFind(obj, path, keySeparator = '.') {
   if (!obj) return undefined;
   if (obj[path]) return obj[path];
-  const paths = path.split(keySeparator);
+  const tokens = path.split(keySeparator);
   let current = obj;
-  for (let i = 0; i < paths.length; ++i) {
-    if (!current) return undefined;
-    if (typeof current[paths[i]] === 'string' && i + 1 < paths.length) {
+  for (let i = 0; i < tokens.length; ) {
+    if (!current || typeof current !== 'object') {
       return undefined;
     }
-    if (current[paths[i]] === undefined) {
-      let j = 2;
-      let p = paths.slice(i, i + j).join(keySeparator);
-      let mix = current[p];
-      while (mix === undefined && paths.length > i + j) {
-        j++;
-        p = paths.slice(i, i + j).join(keySeparator);
-        mix = current[p];
+    let next;
+    let nextPath = '';
+    for (let j = i; j < tokens.length; ++j) {
+      if (j !== i) {
+        nextPath += keySeparator;
       }
-      if (mix === undefined) return undefined;
-      if (mix === null) return null;
-      if (path.endsWith(p)) {
-        if (typeof mix === 'string') return mix;
-        if (p && typeof mix[p] === 'string') return mix[p];
+      nextPath += tokens[j];
+      next = current[nextPath];
+      if (next !== undefined) {
+        i += j - i + 1;
+        break;
       }
-      const joinedPath = paths.slice(i + j).join(keySeparator);
-      if (joinedPath) return deepFind(mix, joinedPath, keySeparator);
-      return undefined;
     }
-    current = current[paths[i]];
+    current = next;
   }
   return current;
 }

test/runtime/eventEmitter.test.js

@@ -27,6 +27,19 @@ describe('i18next', () => {
       expect(disabledHandler).not.toHaveBeenCalled();
     });
 
+    it('should emit twice if a handler was attached twice', () => {
+      const calls = [];
+      const listener = (payload) => {
+        calls.push(payload);
+      };
+
+      emitter.on('events', listener);
+      emitter.on('events', listener);
+      emitter.emit('events', 1);
+
+      expect(calls).toEqual([1, 1]);
+    });
+
     it('it should emit wildcard', () => {
       expect.assertions(2);
 

test/runtime/utils.test.js

@@ -31,4 +31,30 @@ describe('utils', () => {
       expect(res).toEqual({ some: 'thing' });
     });
   });
+
+  describe('#deepFind', () => {
+    it('finds value for a basic path', () => {
+      const obj = { a: { b: { c: 1 } } };
+      const value = utils.deepFind(obj, 'a.b.c');
+      expect(value).toEqual(1);
+    });
+
+    it('finds no value for a non-existent path', () => {
+      const obj = { a: { b: { c: 1 } } };
+      const value = utils.deepFind(obj, 'a.b.d');
+      expect(value).toEqual(undefined);
+    });
+
+    it('finds value for a key that has a dot', () => {
+      const obj = { a: { 'b.b': { c: 1 } } };
+      const value = utils.deepFind(obj, 'a.b.b.c');
+      expect(value).toEqual(1);
+    });
+
+    it('finds value for an array index', () => {
+      const obj = { a: [{ c: 1 }] };
+      const value = utils.deepFind(obj, 'a.0.c');
+      expect(value).toEqual(1);
+    });
+  });
 });