Jakutis' solution

solutions/jakutis.js

@@ -0,0 +1,52 @@
+function countLines(code) {
+  let inComment = false
+  let commentStartedAtLineStart = false
+  let inString = false
+  let inMultilineString = false
+  let newCode = ''
+  for (let i = 0; i < code.length; i++) {
+    if (!inComment && !inString && code[i] === '`' && code[i - 1] !== '\\') {
+      newCode += code[i]
+      inMultilineString = !inMultilineString
+      continue
+    }
+
+    const beforeInComment = inComment
+    if (!inComment && !inString) {
+      if (code[i - 1] === '/' && code[i] === '*') {
+        if (!inMultilineString) {
+          inComment = true
+          commentStartedAtLineStart = code[i - 2] === '\n'
+          newCode = newCode.substr(0, newCode.length - 1)
+        }
+      } else {
+        if (code[i] === '"' || code[i] === "'") {
+          inString = true
+        }
+      }
+    } else if (!inComment && inString) {
+      if (code[i - 1] !== '\\' && (code[i] === '"' && code[i] === "'")) {
+        inString = false
+      }
+    } else if (inComment) {
+      if (code[i - 1] === '*' && code[i] === '/') {
+        inComment = false
+        if (commentStartedAtLineStart && code[i + 1] === '\n') {
+          i++
+        }
+      }
+    }
+    const justClosedComment = beforeInComment && !inComment
+
+    if (!inComment && !justClosedComment) {
+      newCode += code[i]
+    }
+  }
+  newCode = newCode
+    .split('\n')
+    .map(l => l.trim())
+    .filter(l => l && !l.startsWith('//'))
+  return newCode.length
+}
+
+module.exports = countLines;