add exist method

FS.common.js

@@ -15,6 +15,7 @@ var base64 = require('base-64');
 var utf8 = require('utf8');
 
 var _readDir = Promise.promisify(RNFSManager.readDir);
+var _exist = Promise.promisify(RNFSManager.exist);
 var _stat = Promise.promisify(RNFSManager.stat);
 var _readFile = Promise.promisify(RNFSManager.readFile);
 var _writeFile = Promise.promisify(RNFSManager.writeFile);
@@ -81,6 +82,11 @@ var RNFS = {
       })
       .catch(convertError);
   },
+  
+  exist(filepath) {
+    return _exist(filepath)
+      .catch(convertError);
+  },
 
   readFile(filepath, encoding) {
     if (!encoding) encoding = 'utf8';

README.md

@@ -200,6 +200,12 @@ The promise resolves with an array, which contains a boolean and the path that h
 
 Also recursively deletes directories (works like Linux `rm -rf`).
 
+### `promise exist(filepath)`
+
+check if the item exist at `filepath`. If the item does not exist, return false.
+
+The promise resolves with boolean.
+
 ### `promise mkdir(filepath [, excludeFromBackup])`
 
 Create a directory at `filepath`. Automatically creates parents and does not throw if already exists (works like Linux `mkdir -p`).

RNFSManager.m

@@ -56,6 +56,14 @@ RCT_EXPORT_METHOD(readDir:(NSString *)dirPath
   callback(@[[NSNull null], contents]);
 }
 
+RCT_EXPORT_METHOD(exist:(NSString *)filepath
+                  callback:(RCTResponseSenderBlock)callback)
+{
+  BOOL fileExists = [[NSFileManager defaultManager] fileExistsAtPath:filepath];
+
+  callback(@[[NSNull null], [NSNumber numberWithBool:fileExists]]);
+}
+
 RCT_EXPORT_METHOD(stat:(NSString *)filepath
                   callback:(RCTResponseSenderBlock)callback)
 {

android/src/main/java/com/rnfs/RNFSManager.java

@@ -71,6 +71,17 @@ public class RNFSManager extends ReactContextBaseJavaModule {
       callback.invoke(makeErrorPayload(ex));
     }
   }
+  
+  @ReactMethod
+  public void exist(String filepath, Callback callback) {
+    try {
+      File file = new File(filepath);
+      callback.invoke(null, file.exists());
+    } catch (Exception ex) {
+      ex.printStackTrace();
+      callback.invoke(makeErrorPayload(ex));
+    }
+  }
 
   @ReactMethod
   public void readFile(String filepath, Callback callback) {