is-html-equivalent

Assert that an HTML string looks approximately the same as another HTML

Install: npm install is-html-equivalent

Example:

import { assertHtmlIsEquivalent } from 'is-html-equivalent';

const actual = `
  <div class="fe10c23a">
    <h1 class="aab058a7">This is a title</h1>
    <p>This is some text content</p>
  </div>
`;

// I just want to know if there is a highlighted <p> inside a <div>
const expected = `
  <div class="...">
    {{ ... }}
    <p class="highlighted">This is some text content</p>
    {{ ... }}
  </div>
`;

assertHtmlIsEquivalent(actual, expected);

Error: HTML is missing the attribute `class="highlighted"` on the element
``html
<p>This is some text content</p>
``

How this works

This library does much more than assert that the string actual === expected. To start with, it ignores differences in whitespaces in the two strings, but most importantly, it uses expected as a template and checks if actual matches the shape.

isHtmlEquivalent(actual, expected) will check whether the HTML string actual has at least everything that is specified in the HTML string expected. It is certainly valid that actual is much larger and more specific than expected, and for expressing those situations, we use placeholders.

The placeholder syntax is {{ }} and it stands for "some stuff here, either nothing or many elements". Inside the brackets you can write whatever you want, it doesn't get processed, it is just a comment. By including or omitting placeholders we can control what is the HTML shape we expect. Notice the difference between the following examples:

// This means "we expect a <div> with children, where somewhere in the middle
// there is a <p> as a child".
const expected = `
  <div>
    {{ more stuff before the paragraph }}
    <p class="highlighted">This is some text content</p>
    {{ more stuff after the paragraph }}
  </div>
`;

// This means "we expect a <div> with children,
// where THE FIRST child MUST be <p>".
const expected = `
  <div>
    <p class="highlighted">This is some text content</p>
    {{ more stuff after the paragraph }}
  </div>
`;

// This means "we expect a <div> with only one child, which is <p>".
const expected = `
  <div>
    <p class="highlighted">This is some text content</p>
  </div>
`;

API

assertHtmlIsEquivalent: (actual: string, expected: string): void

Tests if actual as an HTML string fits the template described in expected. If it matches, this function returns nothing (undefined), and no other effect happens. If it does not match, an error is thrown describing the mismatch.

isHtmlEquivalent: (actual: string, expected: string): boolean

If you want a simple boolean to indicate the match result, call isHtmlEquivalent(actual, expected). No error is thrown in case of a mismatch.

License

MIT

Thanks

This library uses these dependencies. Thanks to their respective authors:

• diff-dom
• domwalk
• jsdom
• lodash