feat(runtime/os): add Deno.env.has() (#17315)

cli/tests/unit/os_test.ts

@@ -26,6 +26,13 @@ Deno.test({ permissions: { env: true } }, function deleteEnv() {
   assertEquals(Deno.env.get("TEST_VAR"), undefined);
 });
 
+Deno.test({ permissions: { env: true } }, function hasEnv() {
+  Deno.env.set("TEST_VAR", "A");
+  assert(Deno.env.has("TEST_VAR"));
+  Deno.env.delete("TEST_VAR");
+  assert(!Deno.env.has("TEST_VAR"));
+});
+
 Deno.test({ permissions: { env: true } }, function avoidEmptyNamedEnv() {
   assertThrows(() => Deno.env.set("", "v"), TypeError);
   assertThrows(() => Deno.env.set("a=a", "v"), TypeError);

cli/tsc/dts/lib.deno.ns.d.ts

@@ -1231,6 +1231,19 @@ declare namespace Deno {
      */
     delete(key: string): void;
 
+    /** Check whether an environment variable is present or not.
+     *
+     * ```ts
+     * Deno.env.set("SOME_VAR", "Value");
+     * Deno.env.has("SOME_VAR");  // outputs true
+     * ```
+     *
+     * Requires `allow-env` permission.
+     *
+     * @tags allow-env
+     */
+    has(key: string): boolean;
+
     /** Returns a snapshot of the environment variables at invocation as a
      * simple object of keys and values.
      *

runtime/js/30_os.js

@@ -96,6 +96,9 @@
       return ops.op_env();
     },
     set: setEnv,
+    has(key) {
+      return getEnv(key) !== undefined;
+    },
     delete: deleteEnv,
   };