repl: fix pasting after moving the cursor to the left

Fixes: #60446
PR-URL: #60470
Reviewed-By: Jordan Harband <ljharb@gmail.com>

Author: BridgeAR

lib/internal/readline/interface.js

@@ -659,7 +659,17 @@ class Interface extends InterfaceConstructor {
   [kInsertString](c) {
     this[kBeforeEdit](this.line, this.cursor);
     if (!this.isCompletionEnabled) {
-      this.line += c;
+      if (this.cursor < this.line.length) {
+        const beg = StringPrototypeSlice(this.line, 0, this.cursor);
+        const end = StringPrototypeSlice(
+          this.line,
+          this.cursor,
+          this.line.length,
+        );
+        this.line = beg + c + end;
+      } else {
+        this.line += c;
+      }
       this.cursor += c.length;
       this[kWriteToOutput](c);
       return;

test/parallel/test-repl-paste-big-data.js

@@ -9,6 +9,11 @@ const { startNewREPLServer } = require('../common/repl');
 const cpuUsage = process.cpuUsage();
 
 const { replServer } = startNewREPLServer({}, { disableDomainErrorAssert: true });
+replServer.input.emit('data', '{}');
+replServer.input.emit('keypress', '', { name: 'left' });
+replServer.input.emit('data', 'node');
+assert.strictEqual(replServer.line, '{node}');
+
 replServer.input.emit('data', 'a'.repeat(2e4) + '\n');
 replServer.input.emit('data', '.exit\n');