diff --git a/src/utility/check-func.js b/src/utility/check-func.js
new file mode 100644
index 0000000..eb8b0b0
--- /dev/null
+++ b/src/utility/check-func.js
@@ -0,0 +1,15 @@
+function checkPattern(code, pattern) {
+  let i = 0
+  let j = 0
+  while (i < code.length && j < pattern.length) {
+    if (code[i] == pattern[j]) {
+      ++j
+    }
+    ++i
+  }
+  return j == pattern.length
+}
+
+export default {
+  checkPattern,
+}
diff --git a/src/utility/safe-func.js b/src/utility/safe-func.js
new file mode 100644
index 0000000..e6d3c07
--- /dev/null
+++ b/src/utility/safe-func.js
@@ -0,0 +1,72 @@
+import * as t from '@babel/types'
+
+function safeDeleteNode(name, path) {
+  let binding
+  if (path.isFunctionDeclaration()) {
+    binding = path.parentPath.scope.getBinding(name)
+  } else {
+    binding = path.scope.getBinding(name)
+  }
+  if (!binding) {
+    return false
+  }
+  binding.scope.crawl()
+  binding = binding.scope.getBinding(name)
+  if (binding.references) {
+    return false
+  }
+  for (const item of binding.constantViolations) {
+    item.remove()
+  }
+  const decl = binding.path
+  if (decl.removed) {
+    return true
+  }
+  if (!decl.isVariableDeclarator() && !decl.isFunctionDeclaration()) {
+    return true
+  }
+  binding.path.remove()
+  return true
+}
+
+function safeGetLiteral(path) {
+  if (path.isUnaryExpression()) {
+    if (path.node.operator === '-' && path.get('argument').isNumericLiteral()) {
+      return -1 * path.get('argument').node.value
+    }
+    return null
+  }
+  if (path.isLiteral()) {
+    return path.node.value
+  }
+  return null
+}
+
+function safeGetName(path) {
+  if (path.isIdentifier()) {
+    return path.node.name
+  }
+  if (path.isLiteral()) {
+    return path.node.value
+  }
+  return null
+}
+
+function safeReplace(path, value) {
+  if (typeof value === 'string') {
+    path.replaceWith(t.stringLiteral(value))
+    return
+  }
+  if (typeof value === 'number') {
+    path.replaceWith(t.numericLiteral(value))
+    return
+  }
+  path.replaceWithSourceString(value)
+}
+
+export default {
+  safeDeleteNode,
+  safeGetLiteral,
+  safeGetName,
+  safeReplace,
+}