Added equals.md and tests

snippets/equals.md

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+### equals
+
+Performs a deep comparison between two values to determine if they are equivalent.
+
+Check if the two values are identical, if they are both `Date` objects with the same time, using `Date.getTime()` or if they are both non-object values with an equivalent value (non-strict comparison).
+Check if only one value is `null` or `undefined` or if their prototypes differ.
+If none of the above conditions are met, use `Object.keys()` to check if both values have the same number of keys, then use `Array.every()` to check if every key in the first value exists in the second one and if they are equivalent by calling this method recursively.
+
+```js
+const equals = (a, b) => {
+  if (a === b) return true;
+  if (a instanceof Date && b instanceof Date)
+    return a.getTime() === b.getTime();
+  if (!a || !b || (typeof a != 'object' && typeof b !== 'object'))
+    return a == b;
+  if (a === null || a === undefined || b === null || b === undefined)
+    return false;
+  if (a.prototype !== b.prototype) return false;
+  let keys = Object.keys(a);
+  if (keys.length !== Object.keys(b).length) return false;
+  return keys.every(k => equals(a[k], b[k]));
+};
+```
+
+```js
+equals({ a: [2, {e: 3}], b: [4], c: 'foo' }, { a: [2, {e: 3}], b: [4], c: 'foo' }); // true
+```