Added comments to FieldsArea class and its methods

fields.js

@@ -1,10 +1,25 @@
 const schema = require("./schema");
 
+/**
+ * Pass fields area to be used as pass lower level keys
+ * @see https://apple.co/2wkUBd
+ */
+
 class FieldsArea {
 	constructor() {
 		this.fields = [];
 	}
 
+	/**
+	 * A wrapper of Array.prototype.push to validate the pushed content with the schema.
+	 * Accepts also one array of objects.
+	 *
+	 * @method push
+	 * @params {Object[]} fields - the fields to be checked and pushed
+	 * @params {schema.constants.field} fields[].* - each key must be compliant with schema.constants.field structure
+	 * @returns {Number} - the amount of pushed elements (for checks)
+	 */
+
 	push(...fields) {
 		if (fields[0] instanceof Array && fields[0].length) {
 			fields = fields[0];
@@ -17,6 +32,15 @@ class FieldsArea {
 		return validFields.length;
 	}
 
+	/**
+	 * A wrapper of Array.prototype.pop and Array.prototype.slice to pop
+	 * last element or n elements starting from the end.
+	 *
+	 * @method pop
+	 * @params {Number} [quantity=-1] - the amount of elements to be removed
+	 * @returns {Number} - the amount of removed elements
+	 */
+
 	pop(quantity = -1) {
 		if (!this.fields.length) {
 			return undefined;