search api desc & return empty string for empty match

binding/javascript/ReadMe.md

@@ -7,6 +7,13 @@
 npm install ip2region.js --save 
 ```
 
+### 关于查询 API
+查询 API 的原型为：
+```javascript
+search(ip: string | Buffer): string;
+```
+如果查询出错会抛异常，查询成功则会返回字符的 `region` 信息，如果指定的 IP 查询不到则会返回空字符串 `""`。
+
 ### 关于 IPv4 和 IPv6
 该 xdb 查询客户端实现同时支持对 IPv4 和 IPv6 的查询，使用方式如下：
 ```javascript

binding/javascript/package.json

@@ -1,6 +1,6 @@
 {
   "name": "ip2region.js",
-  "version": "3.1.5",
+  "version": "3.1.6",
   "description": "official javascript binding for ip2region with both IPv4 and IPv6 supported ",
   "type": "module",
   "main": "index.js",

binding/javascript/searcher.js

@@ -70,7 +70,7 @@ export class Searcher {
         const bytes = ipBytes.length, dBytes = ipBytes.length << 1;
         const indexSize = this.version.indexSize;
         const buff = Buffer.alloc(indexSize);
-        let dLen = -1, dPtr = -1, l = 0, h = (ePtr - sPtr) / indexSize;
+        let dLen = 0, dPtr = 0, l = 0, h = (ePtr - sPtr) / indexSize;
         while (l <= h) {
             const m = (l + h) >> 1;
             const p = sPtr + m * indexSize;
@@ -90,8 +90,8 @@ export class Searcher {
 
         // empty match interception.
         // and this could be a case.
-        if (dPtr == -1) {
+        if (dLen == 0) {
-            return null;
+            return "";
         }
 
         // console.log(`dLen: ${dLen}, dPtr: ${dPtr}`);