Remove type declaration file and add type guard in caught error

- This should resolve GH-34

Author: izolate

index.d.ts

@@ -1,4 +1,4 @@
-import { defaultOptions } from "./options";
+import { defaultOptions, MillifyOptions } from "./options";
 import { parseValue, roundTo } from "./utils";
 
 // Most commonly used digit grouping base.
@@ -49,8 +49,10 @@ function millify(value: number, options?: Partial<MillifyOptions>): string {
   let val: number;
   try {
     val = parseValue(value);
-  } catch (e: any) {
-    console.warn(`WARN: ${e.message} (millify)`);
+  } catch (e) {
+    if (e instanceof Error) {
+      console.warn(`WARN: ${e.message} (millify)`);
+    }
     // Invalid values will be converted to string as per `String()`.
     return String(value);
   }

lib/millify.ts

@@ -1,3 +1,29 @@
+/**
+ * Options used to configure Millify.
+ */
+export interface MillifyOptions {
+  /**
+   * The number of significant figures.
+   */
+  precision: number;
+  /**
+   * The type of decimal marker (e.g. period ".").
+   */
+  decimalSeparator: string;
+  /**
+   * Convert units to lower case.
+   */
+  lowercase: boolean;
+  /**
+   * Add a space between the number and the unit.
+   */
+  space: boolean;
+  /**
+   * A list of units to use.
+   */
+  units: string[];
+}
+
 /**
  * Default options for Millify.
  */