add WriteString method

README.md

@@ -1,9 +1,11 @@
 # xk6-file
-A [k6](https://github.com/loadimpact/k6) extension for writing files, implemented using the 
+[k6](https://github.com/loadimpact/k6) extension for writing files, implemented using the 
 [xk6](https://github.com/k6io/xk6) system.
 
 ## Build
-`xk6 build v0.31.1 --with github.com/avitalique/xk6-file`
+```shell
+xk6 build v0.31.1 --with github.com/avitalique/xk6-file
+```
 
 ## Example
 ```javascript
@@ -12,6 +14,7 @@ import file from 'k6/x/file';
 const filepath = 'sample-output.txt';
 
 export default function () {
-    file.appendString(filepath, `Some text. VU: ${__VU}  -  ITER: ${__ITER}\n`);
+    file.writeString(filepath, 'New file. First line.\n');
+    file.appendString(filepath, `Second line. VU: ${__VU}  -  ITER: ${__ITER}`);
 }
 ```

file.go

@@ -14,10 +14,24 @@ func init() {
 	modules.Register("k6/x/file", new(FILE))
 }
 
-// FILE is the k6 extension.
+// FILE is the k6 extension
 type FILE struct{}
 
-// Append a string to file
+// Write string to file
+func (*FILE) WriteString(path string, s string) error {
+	f, err := os.Create(path)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	if _, err := f.WriteString(s); err != nil {
+		return err
+	}
+	return nil
+}
+
+// Append string to file
 func (*FILE) AppendString(path string, s string) error {
 	f, err := os.OpenFile(path,
 		os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)

sample-script.js

@@ -3,5 +3,6 @@ import file from 'k6/x/file';
 const filepath = 'sample-output.txt';
 
 export default function () {
-    file.appendString(filepath, `Some text. VU: ${__VU}  -  ITER: ${__ITER}\n`);
+    file.writeString(filepath, 'New file. First line.\n');
+    file.appendString(filepath, `Second line. VU: ${__VU}  -  ITER: ${__ITER}`);
 }