extract internal method isSubdir to fs/utils.ts (denoland/deno_std#285)

Original: https://github.com/denoland/deno_std/commit/da4abcd9a3a5775939c3941a884d1c6f4d287d0f

1 files changed, 23 insertions, 0 deletions

diff --git a/fs/utils.ts b/fs/utils.ts
new file mode 100644
index 000000000..dd7ee5fa4
--- /dev/null
+++ b/fs/utils.ts
@@ -0,0 +1,23 @@
+import * as path from "./path/mod.ts";
+
+/**
+ * Test whether or not `dest` is a sub-directory of `src`
+ * @param src src file path
+ * @param dest dest file path
+ * @param sep path separator
+ */
+export function isSubdir(
+  src: string,
+  dest: string,
+  sep: string = path.sep
+): boolean {
+  if (src === dest) {
+    return false;
+  }
+  const srcArray = src.split(sep);
+  const destArray = dest.split(sep);
+
+  return srcArray.reduce((acc, current, i) => {
+    return acc && destArray[i] === current;
+  }, true);
+}