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dom-compare

Build Status Coverage Status NPM version Dependency Status

Breaking changes. v0.3.0 requires node version >=0.10

NodeJS module to compare two DOM-trees

DOM Comparison

Consider two documents. Expected:

<document>
    <!-- comment -->
    <element attribute="10" attributeX="100">
        <text>  text content </text>
        <inner>
            <node />
        </inner>
    </element>
    <![CDATA[  cdata node]]>
</document>

and actual one:

<document>
    <element attribute="100">
        <text>text content</text>
        <inner />
        <inner2 />
    </element>
    <![CDATA[cdata node  ]]>
</document>

One can compare them, get the result (is them equals, or not), and get extended report (why them are different).

var compare = require('dom-compare').compare,
    reporter = require('dom-compare').GroupingReporter,
    expected = ..., // expected DOM tree
    actual = ..., // actual one
    result, diff, groupedDiff;

// compare to DOM trees, get a result object
result = compare(expected, actual);

// get comparison result
console.log(result.getResult()); // false cause' trees are different

// get all differences
diff = result.getDifferences(); // array of diff-objects

// differences, grouped by node XPath
grouped = reporter.getDifferences(result); // object, key - node XPATH, value - array of differences (strings)

// string representation
console.log(report.report(result));

Diff-object has a following form:

{
    node: "/document/element",
    message: "Attribute 'attribute': expected value '10' instead of '100'";
}

By using GroupingReporter one can get a result of a following type

{
    '/document/element': [
        "Attribute 'attribute': expected value '10' instead of '100'",
        "Extra attribute 'attributeX'"
    ]    
}

Comparison options

Comparison function can take a third argument with options like this:

var options = {
    stripSpaces: true,
    compareComments: true
};

result = compare(expected, actual, options);

Comments comparison

By default, all comments are ignored. Set compareComments options to true to compare them too.

Whitespace comparison

By default, all text nodes (text, CDATA, comments if enabled as mentioned above) compared with respect to leading and trailing whitespaces. Set stripSpaces option to true to automatically strip spaces in text and comment nodes. This option doesn't change the way CDATA sections is compared, they are always compared with respect to whitespaces.

Custom comparators (since 0.3)

This is experimental feature and may change in future releases

Sometimes one needs a special rules to compare some DOM elements.

Imagine you have some nodes with config attr which contains JSON data (see samples/json-compare). So, if you'd like to compare such documents, you will see something like this:

/document/div
	Attribute 'config': expected value '{"attr1":10,"attr2":30,"attr3":-1}' instead of '{"attr1":10,"attr2":20}'

This makes not much sense... You can use custom comparators option!

var domcompare = require('dom-compare');

// create comparator for specified node name
// you can specify multiple node names here - pass multiple arguments
var configComparator = domcompare.comparators.jsonComparator('config')

var res = domcompare.compare(treeA, treeB, {
    comparators: {
        // for every attrbute difference, run custom comparison routine
        // you can pass multiple comparators here using array
        ATTRIBUTE_NODE: configComparator
    }
});

Bundled JSON comparator can parse node's value like JSON, and if it's parsed, compare using rfc6902-json-diff library. Using comparators, you can get result like this:

/document/div
	Attribute "config" differs. Expected:
		{
		  "attr1": 10,
		  "attr2": 20
		}
		Actual:
		{
		  "attr1": 10,
		  "attr2": 30,
		  "attr3": -1
		}
		Diff:
		[
		  {
		    "op": "replace",
		    "path": "/attr2",
		    "value": 20
		  },
		  {
		    "op": "remove",
		    "path": "/attr3"
		  }
		]
Writing custom comparators

The comparator is a function. It receives two arguments: expected node and actual node.

Comparators can return following values:

  • any falsy value - skip to next comparator or (if no any) proceed as regular
  • true - ignore any differences, continue comparison
  • non empty string - difference found, string is treated as error message
  • object with fields:
    • message - error message as above,
    • stop - boolean flag, set to true to stop further comparison

See lib/comparators/jsonComparator.js for a working example.

Cli utility

When installed globally with npm install -g dom-compare cli utility is available. See usage information and command-line options with domcompare --help

You can try it on bundled samples:

  $ cd samples
  $ domcompare -s ./expected.xml ./actual.xml
  Documents are not equal
  /document/element
      Attribute 'attribute': expected value '10' instead of '100'
      Attribute 'attributeX' is missed
      Extra element 'inner2'
  /document/element/inner
      Element 'node' is missed
  /document
      Expected CDATA value '  cdata node' instead of 'cdata node  '

DOM Canonic Form

Implemented as XMLSerializer interface

Simple rules

  1. Every node (text, node, attribute) on a new line
  2. Empty tags - in a short form
  3. Node indent - 4 spaces, attribute indent - 2 spaces
  4. Attributes are sorted alphabetically
  5. Attribute values are serialized in double quotes

Consider the following XML-document...

<document>
  <element>DOM Compare</element>
  <emptyNode></emptyNode>
  <element attribute1="value" attribute2="value">
    <element>Text node</element>
  </element>
</document>

...and code snippet...

var canonizingSerializer = new (require('dom-compare').XMLSerializer)();
var doc = ...; // parse above document somehow 
console.log(canonizingSerializer.serializeToString(doc));

You'll receive the following output

<document>
    <element>
        DOM Compare
    </element>
    <emptyNode />
    <element
      attribute1="value"
      attribute2="value">
        <element>
            Text node
        </element>
    </element>
</document>