fix: error patterns and string building in sif.go and js/scan.go

replace errors.new(fmt.sprintf()) with fmt.errorf, use strings.builder
instead of string concatenation in loop, fix defer in loop issue,
preallocate slices where size is estimable

pkg/scan/js/scan.go

@@ -14,7 +14,6 @@ package js
 
 import (
 	"bufio"
-	"fmt"
 	"io"
 	"net/http"
 	"os"
@@ -44,17 +43,17 @@ func JavascriptScan(url string, timeout time.Duration, threads int, logdir strin
 	}
 	resp, err := http.Get(url)
 	if err != nil {
-		fmt.Println(err)
 		return nil, err
 	}
 	defer resp.Body.Close()
 
-	var html string
+	var sb strings.Builder
 	scanner := bufio.NewScanner(resp.Body)
 	scanner.Split(bufio.ScanLines)
 	for scanner.Scan() {
-		html += scanner.Text()
+		sb.WriteString(scanner.Text())
 	}
+	html := sb.String()
 
 	doc, err := htmlquery.Parse(strings.NewReader(html))
 	if err != nil {
@@ -99,19 +98,20 @@ func JavascriptScan(url string, timeout time.Duration, threads int, logdir strin
 
 	jslog.Infof("Got %d scripts, now running scans on them", len(scripts))
 
-	var supabaseResults []supabaseScanResult
+	supabaseResults := make([]supabaseScanResult, 0, len(scripts))
 	for _, script := range scripts {
 		jslog.Infof("Scanning %s", script)
 		resp, err := http.Get(script)
 		if err != nil {
-			fmt.Println(err)
+			jslog.Warnf("Failed to fetch script: %s", err)
 			continue
 		}
-		defer resp.Body.Close()
 
 		bodyBytes, err := io.ReadAll(resp.Body)
+		resp.Body.Close()
 		if err != nil {
-			log.Fatal(err)
+			jslog.Errorf("Failed to read script body: %s", err)
+			continue
 		}
 		content := string(bodyBytes)
 

sif.go

@@ -18,7 +18,6 @@ package sif
 import (
 	"bufio"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"os"
 	"strings"
@@ -81,7 +80,7 @@ func New(settings *config.Settings) (*App, error) {
 			app.targets = append(app.targets, scanner.Text())
 		}
 	} else {
-		return app, errors.New("target(s) must be supplied with -u or -f\n\nSee 'sif -h' for more information")
+		return app, fmt.Errorf("target(s) must be supplied with -u or -f\n\nSee 'sif -h' for more information")
 	}
 
 	return app, nil
@@ -105,16 +104,16 @@ func (app *App) Run() error {
 		defer logger.Close()
 	}
 
-	scansRun := []string{}
+	scansRun := make([]string, 0, 16)
 
 	for _, url := range app.targets {
 		if !strings.Contains(url, "://") {
-			return errors.New(fmt.Sprintf("URL %s must include leading protocol", url))
+			return fmt.Errorf("URL %s must include leading protocol", url)
 		}
 
 		log.Infof("📡Starting scan on %s...", url)
 
-		moduleResults := []ModuleResult{}
+		moduleResults := make([]ModuleResult, 0, 16)
 
 		if app.settings.LogDir != "" {
 			if err := logger.CreateFile(&app.logFiles, url, app.settings.LogDir); err != nil {