LibWeb: Implement Range.collapse

Author: https://github.com/Lubrsi
Commit: https://github.com/SerenityOS/serenity/commit/2b2dbdc74f
Pull-request: https://github.com/SerenityOS/serenity/pull/12774

Userland/Libraries/LibWeb/DOM/Range.cpp

@@ -345,6 +345,20 @@ ExceptionOr<void> Range::select_node(Node& node)
     return select(node);
 }
 
+// https://dom.spec.whatwg.org/#dom-range-collapse
+void Range::collapse(bool to_start)
+{
+    // The collapse(toStart) method steps are to, if toStart is true, set end to start; otherwise set start to end.
+    if (to_start) {
+        m_end_container = m_start_container;
+        m_end_offset = m_start_offset;
+        return;
+    }
+
+    m_start_container = m_end_container;
+    m_start_offset = m_end_offset;
+}
+
 NonnullRefPtr<Range> Range::clone_range() const
 {
     return adopt_ref(*new Range(const_cast<Node&>(*m_start_container), m_start_offset, const_cast<Node&>(*m_end_container), m_end_offset));

Userland/Libraries/LibWeb/DOM/Range.h

@@ -31,6 +31,7 @@ public:
     ExceptionOr<void> set_end_before(Node& node);
     ExceptionOr<void> set_end_after(Node& node);
     ExceptionOr<void> select_node(Node& node);
+    void collapse(bool to_start);
 
     // https://dom.spec.whatwg.org/#dom-range-start_to_start
     enum HowToCompareBoundaryPoints : u16 {

Userland/Libraries/LibWeb/DOM/Range.idl

@@ -14,6 +14,7 @@ interface Range : AbstractRange {
     undefined setStartAfter(Node node);
     undefined setEndBefore(Node node);
     undefined setEndAfter(Node node);
+    undefined collapse(optional boolean toStart = false);
     undefined selectNode(Node node);
 
     const unsigned short START_TO_START = 0;