Implement null-filling on no match

Author: stefanmaric

lib/errors.js

@@ -1,4 +1,14 @@
 
+class ModelError extends Error {
+  constructor(...args) {
+    super(...args)
+
+    if (Error.captureStackTrace) Error.captureStackTrace(this, ModelError)
+
+    this.name = 'ModelError'
+  }
+}
+
 class UnknownFilterError extends Error {
   constructor(...args) {
     super(...args)
@@ -10,5 +20,6 @@ class UnknownFilterError extends Error {
 }
 
 module.exports = {
+  ModelError,
   UnknownFilterError,
 }

lib/extract.js

@@ -1,7 +1,7 @@
 const cssSelect = require('css-select')
 const { DomHandler, Parser } = require('htmlparser2')
 
-const { UnknownFilterError } = require('./errors')
+const { ModelError, UnknownFilterError } = require('./errors')
 const filters = require('./filters')
 const getters = require('./getters')
 const { DOMHANDLER_OPTIONS, HTMLPARSER2_OPTIONS } = require('./options')
@@ -22,7 +22,7 @@ const {
  */
 
 function extract(html, model, options = {}) {
-  // Using Object.assig instead of object spread removes the need of null checks.
+  // Using Object.assign instead of object spread removes the need of null checks.
   const parserOptions = Object.assign({}, HTMLPARSER2_OPTIONS, options.htmlparser2)
   const handlerOptions = Object.assign({}, DOMHANDLER_OPTIONS, options.domhandler)
 
@@ -44,31 +44,44 @@ function extract(html, model, options = {}) {
  */
 
 function getItem(dom, item) {
-  let data
-
   if (isArray(item)) {
     const query = parseQuery(item[0])
     const matches = cssSelect.selectAll(query.selector, dom)
 
+    if (!matches || !matches.length) return null
+
     if (isArray(item[1]) || isObject(item[1])) {
-      data = matches.map((context) => getItem(context, item[1]))
-    } else {
-      data = matches.map(resolveGetter(getters, query)).map(applyFilters.bind(null, filters, query))
+      return matches.map((context) => getItem(context, item[1]))
     }
-  } else if (isObject(item)) {
-    data = Object.keys(item).reduce((acc, key) => {
+
+    return matches.map((node) => {
+      const data = resolveGetter(getters, query)(node)
+      return applyFilters(filters, query, data)
+    })
+  }
+
+  if (isObject(item)) {
+    return Object.keys(item).reduce((acc, key) => {
       acc[key] = getItem(dom, item[key])
       return acc
     }, {})
-  } else if (isString(item)) {
+  }
+
+  if (isString(item)) {
     const query = parseQuery(item)
-    const matches = cssSelect.selectOne(query.selector, dom)
+    const match = cssSelect.selectOne(query.selector, dom)
+
+    if (!match) return null
+
+    const data = resolveGetter(getters, query)(match)
 
-    data = resolveGetter(getters, query)(matches)
-    data = applyFilters(filters, query, data)
+    return applyFilters(filters, query, data)
   }
 
-  return data
+  const unsupportedType = item === null ? 'null' : typeof item
+  throw new ModelError(
+    `The model has to be a string, an Object or an Array; got ${unsupportedType} instead.`
+  )
 }
 
 /**