script_tag: cosmetic for value-less attributes

Some attributes are usually written without values, for example :
`<script defer async src="..." />`

This is purely cosmetic as the attribute should also be accepted with an empty
value or a value identical to the attribute's name :
https://dev.w3.org/html5/pf-summary/infrastructure.html#boolean-attribute

system/Helpers/html_helper.php

@@ -207,11 +207,12 @@ function script_tag($src = '', bool $indexPage = false): string
                     $script .= 'src="' . slash_item('baseURL') . $v . '" ';
                 }
             } else {
-                $script .= $k . '="' . $v . '" ';
+                // for attributes without values, like async or defer, use NULL.
+                $script .= $k . (is_null($v) ? ' ' : '="' . $v . '" ');
             }
         }
 
-        return $script . 'type="text/javascript"' . '></script>';
+        return $script . 'type="text/javascript"></script>';
     }
 }
 

tests/system/Helpers/HTMLHelperTest.php

@@ -248,6 +248,27 @@ public function testScriptTagWithIndexpage()
         $this->assertSame($expected, script_tag($target, true));
     }
 
+    public function testScriptTagWithSrc()
+    {
+        $target   = [ 'src' => 'http://site.com/js/mystyles.js' ];
+        $expected = '<script src="http://site.com/js/mystyles.js" type="text/javascript"></script>';
+        $this->assertSame($expected, script_tag($target));
+    }
+
+    public function testScriptTagWithSrcWithoutProtocol()
+    {
+        $target   = [ 'src' => 'js/mystyles.js' ];
+        $expected = '<script src="http://example.com/js/mystyles.js" type="text/javascript"></script>';
+        $this->assertSame($expected, script_tag($target));
+    }
+
+    public function testScriptTagWithSrcAndAttributes()
+    {
+        $target   = [ 'src' => 'js/mystyles.js', 'charset' => 'UTF-8', 'defer' => '', 'async' => null ];
+        $expected = '<script src="http://example.com/js/mystyles.js" charset="UTF-8" defer="" async type="text/javascript"></script>';
+        $this->assertSame($expected, script_tag($target));
+    }
+
     public function testLinkTag()
     {
         $target   = 'css/mystyles.css';

user_guide_src/source/helpers/html_helper/011.php

@@ -1,6 +1,6 @@
 <?php
 
-$script = ['src' => 'js/printer.js'];
+$script = ['src' => 'js/printer.js', 'defer' => null];
 
 echo script_tag($script);
-// <script src="http://site.com/js/printer.js" type="text/javascript"></script>
+// <script src="http://site.com/js/printer.js" defer type="text/javascript"></script>