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Author: stdlib-bot

README.md

@@ -83,11 +83,22 @@ var out = replaceBefore( 'beep boop', ' ', 'loop', 0 );
 
 out = replaceBefore( 'beep boop', 'o', 'bar', 0 );
 // returns 'baroop'
+```
+
+To begin searching from a specific index, provide a corresponding `fromIndex` argument.
 
-out = replaceBefore( 'beep boop', 'p', 'bar', 5 );
+```javascript
+var out = replaceBefore( 'beep boop', 'p', 'bar', 5 );
 // returns 'barp'
 ```
 
+If `fromIndex` is less than zero, the starting index is resolved relative to the last string character, with the last string character corresponding to `fromIndex = -1`.
+
+```javascript
+var out = replaceBefore( 'beep boop beep', ' ', 'loop', -6 );
+// returns 'loop beep'
+```
+
 </section>
 
 <!-- /.usage -->
@@ -100,7 +111,7 @@ out = replaceBefore( 'beep boop', 'p', 'bar', 5 );
 
 -   If a search string is not present in a provided string, the function returns the provided string unchanged.
 -   If a search string is an empty string, the function returns the provided string unchanged.
--   If `fromIndex` is less than `0` or greater than `str.length`, the search starts at index `0` and `str.length`, respectively.
+-   If `fromIndex` resolves to an index which is greater than or equal to `str.length`, the function returns the provided string unchanged.
 
 </section>
 

dist/index.js

@@ -1,7 +1,10 @@
 
 {{alias}}( str, search, replacement, fromIndex )
     Replaces the substring before the first occurrence of a specified search
-    string. 
+    string.
+
+    If unable to find a search string, the function returns the input string
+    unchanged.
 
     Parameters
     ----------
@@ -15,7 +18,9 @@
         Replacement string.
 
     fromIndex: integer
-        Index from which to start the search.
+        Starting index (inclusive). If less than zero, the starting index is
+        resolved relative to the last string character, with the last string
+        character corresponding to `fromIndex = -1`.
 
     Returns
     -------

dist/index.js.map

@@ -21,6 +21,11 @@
 /**
 * Replaces the substring before the first occurrence of a specified search string.
 *
+* ## Notes
+*
+* -   If unable to find search string, the function returns the input string unchanged.
+* -   If `fromIndex` is less than zero, the starting index is resolved relative to the last string character, with the last string character corresponding to `fromIndex = -1`.
+*
 * @param str - input string
 * @param search - search string
 * @param replacement - replacement string

docs/repl.txt

@@ -48,9 +48,9 @@
 function replaceBefore( str, search, replacement, fromIndex ) {
 	var idx;
 	if ( fromIndex < 0 ) {
-		fromIndex = 0;
-	} else if ( fromIndex > str.length ) {
-		fromIndex = str.length;
+		fromIndex += str.length;
+	} else if ( fromIndex >= str.length ) {
+		return str;
 	}
 	idx = str.indexOf( search, fromIndex );
 	if ( str === '' || search === '' || replacement === '' || idx < 0 ) {

docs/types/index.d.ts

@@ -87,14 +87,24 @@ tape( 'the function replaces the substring before a provided search string (cust
 
 	str = 'beep boop baz';
 	actual = replaceBefore( str, 'beep', 'foo', -2 );
-	expected = 'foobeep boop baz';
+	expected = 'beep boop baz';
+	t.strictEqual( actual, expected, 'returns expected value' );
+
+	str = 'beep boop baz';
+	actual = replaceBefore( str, 'baz', 'foo', -5 );
+	expected = 'foobaz';
 	t.strictEqual( actual, expected, 'returns expected value' );
 
 	str = 'beep boop baz';
 	actual = replaceBefore( str, 'beep', 'foo', 20 );
 	expected = 'beep boop baz';
 	t.strictEqual( actual, expected, 'returns expected value' );
 
+	str = 'beep boop baz';
+	actual = replaceBefore( str, 'beep', 'foo', -200 );
+	expected = 'foobeep boop baz';
+	t.strictEqual( actual, expected, 'returns expected value' );
+
 	t.end();
 });