Add docstrings for route builder service (#9118)

* add docstrings for route builder service

services/route-builder.js

@@ -1,3 +1,9 @@
+/**
+ * Common functions and utilities for tasks related to route building
+ *
+ * @module
+ */
+
 import toArray from '../core/base-service/to-array.js'
 
 /*
@@ -9,24 +15,47 @@ import toArray from '../core/base-service/to-array.js'
  * haven't done so yet.
  */
 export default class RouteBuilder {
+  /**
+   * Creates a RouteBuilder object.
+   *
+   * @param {object} attrs - Refer to individual attributes
+   * @param {string} attrs.base - Base URL, defaults to ''
+   */
   constructor({ base = '' } = {}) {
     this.base = base
 
     this._formatComponents = []
     this.capture = []
   }
 
+  /**
+   * Get the format components separated by '/'
+   *
+   * @returns {string} Format components, for example: "format1/format2/format3"
+   */
   get format() {
     return this._formatComponents.join('/')
   }
 
+  /**
+   * Saves the format and capture values in the RouteBuilder instance.
+   *
+   * @param {string} format - Pattern based on path-to-regex, for example: (?:(.+)\\.)?${serviceBaseUrl}
+   * @param {string} capture - Value to capture
+   * @returns {object} RouteBuilder instance for chaining
+   */
   push(format, capture) {
     this._formatComponents = this._formatComponents.concat(toArray(format))
     this.capture = this.capture.concat(toArray(capture))
     // Return `this` for chaining.
     return this
   }
 
+  /**
+   * Returns a new object based on RouteBuilder instance containing its base, format and capture properties.
+   *
+   * @returns {object} Object containing base, format and capture properties of the RouteBuilder instance
+   */
   toObject() {
     const { base, format, capture } = this
     return { base, format, capture }