feat: added isTypeof method

it asserts that a target object is of a given type if all the given props are
defined in the target object

src/index.ts

@@ -22,6 +22,23 @@ export const CASE_STYLES = {
     SNAKE_CASE: 2
 };
 
+/**
+ * picks the given value from the object, supressing any error that may occur while trying
+ * to access key
+ *
+ * @param key
+ * @param object
+ */
+const _pickValue = (key: string, object: object) => {
+    try {
+        const value = object[key];
+        return value;
+    }
+    catch(ex) {
+        return undefined;
+    }
+};
+
 /**
  * tests if argument is null
  */
@@ -127,7 +144,6 @@ export const isParameter = (arg: any, isNullable: boolean = true) => {
 
     return true;
 };
-
 /**
  * puts argument into an array if it is not an array,
  */
@@ -155,6 +171,16 @@ export function makeObject<T>(arg: any): T {
     return {} as T;
 };
 
+/**
+ * asserts that target is T if the given property is defined in target
+ * @param prop property to check
+ * @param target the target object
+ */
+export const isTypeOf = <T extends O, O extends object = any>(props: string | string[], target: O): target is T => {
+    return makeArray(props).every(prop => typeof _pickValue(prop, target) !== 'undefined');
+}
+
+
 /**
  * returns true if key is not set in the given object or key is set and its value is truthy
  */
@@ -169,23 +195,6 @@ export const keySetAndTrue = (key: string, object: object): boolean => {
     return typeof object[key] !== 'undefined' && !!object[key];
 };
 
-/**
- * picks the given value from the object, supressing any error that may occur while trying
- * to access key
- *
- * @param key
- * @param object
- */
-const _pickValue = (key: string, object: object) => {
-    try {
-        const value = object[key];
-        return value;
-    }
-    catch(ex) {
-        return undefined;
-    }
-};
-
 /**
  * returns the value for the first key that exists in the object otherwise,
  * it returns the default value

tests/index.spec.ts

@@ -182,6 +182,18 @@ describe('Utils', function() {
         });
     });
 
+    describe(`.isTypeof<T extends O, O extends object = any>(props: string | string, target: O): target is T`, function() {
+        it(`should assert that target is of type T if all the given props are defined in the
+            target object`, function() {
+            expect(Utils.isTypeOf<Array<number>>('length', [])).toEqual(true);
+        });
+
+        it(`should assert that target is not of type T if any of the given props is not defined in
+            the target object`, function() {
+            expect(Utils.isTypeOf<Array<number>>('len', [])).toEqual(false);
+        });
+    });
+
     describe('.deleteProperty(key: string, target: object): boolean', function() {
         it(`should delete the given property from the target object`, function() {
             const target = {name: 'name'};