playwright/docs/selectors.md
Arjun Attam ee98bd0a29
docs(selectors): update structure and add best practices (#3817)
* docs(selectors): update structure and add best practices

* dgozman comments
2020-09-09 17:14:33 -07:00

10 KiB

Element selectors

Selectors query elements on the web page for interactions, like page.click, and to obtain ElementHandle through page.$. Built-in selectors auto-pierce shadow DOM.

Syntax

Selectors are defined by selector engine name and selector body, engine=body.

Body format is assumed to ignore leading and trailing white spaces, so that extra whitespace can be added for readability.

Short-forms

For convenience, common selectors have short-forms:

  • Selector starting with // or .. is assumed to be xpath=selector
    • Example: page.click('//html') is converted to page.click('xpath=//html').
  • Selector starting and ending with a quote (either " or ') is assumed to be text=selector
    • Example: page.click('"foo"') is converted to page.click('text="foo"').
  • Otherwise, selector is assumed to be css=selector
    • Example: page.click('div') is converted to page.click('css=div').

Chaining selectors

Selectors defined as engine=body or in short-form can be combined with the >> token, e.g. selector1 >> selector2 >> selectors3. When selectors are chained, next one is queried relative to the previous one's result.

For example,

css=article >> css=.bar > .baz >> css=span[attr=value]

is equivalent to

document
  .querySelector('article')
  .querySelector('.bar > .baz')
  .querySelector('span[attr=value]')

If a selector needs to include >> in the body, it should be escaped inside a string to not be confused with chaining separator, e.g. text="some >> text".

Intermediate matches

By default, chained selectors resolve to an element queried by the last selector. A selector can be prefixed with * to capture elements that are queried by an intermediate selector.

For example, css=article >> text=Hello captures the element with the text Hello, and *css=article >> text=Hello (note the *) captures the article element that contains some element with the text Hello.

Best practices

The choice of selectors determines the resiliency of automation scripts. To reduce the maintenance burden, we recommend prioritizing user-facing attributes and explicit contracts.

Prioritize user-facing attributes

Attributes like text content, input placeholder, accessibility roles and labels are user-facing attributes that change rarely. These attributes are not impacted by DOM structure changes.

The following examples use the built-in text and css selector engines.

// queries "Login" text selector
await page.click('text="Login"');
await page.click('"Login"'); // short-form

// queries "Search GitHub" placeholder attribute
await page.fill('css=[placeholder="Search GitHub"]');
await page.fill('[placeholder="Search GitHub"]'); // short-form

// queries "Close" accessibility label
await page.click('css=[aria-label="Close"]');
await page.click('[aria-label="Close"]'); // short-form

// combine role and text queries
await page.click('css=nav >> text=Login');

Define explicit contract

When user-facing attributes change frequently, it is recommended to use explicit test ids, like data-test-id. These data-* attributes are supported by the css and id selectors.

<button data-test-id="directions">Itinéraire</button>
// queries data-test-id attribute with css
await page.click('css=[data-test-id=directions]');
await page.click('[data-test-id=directions]'); // short-form

// queries data-test-id with id
await page.click('data-test-id=directions');

Avoid selectors tied to implementation

xpath and css can be tied to the DOM structure or implementation. These selectors can break when the DOM structure changes.

// avoid long css or xpath chains
await page.click('#tsf > div:nth-child(2) > div.A8SBwf > div.RNNXgb > div > div.a4bIc > input');
await page.click('//*[@id="tsf"]/div[2]/div[1]/div[1]/div/div[2]/input');

Examples

// queries 'div' css selector
const handle = await page.$('css=div');

// queries '//html/body/div' xpath selector
const handle = await page.$('xpath=//html/body/div');

// queries '"foo"' text selector
const handle = await page.$('text="foo"');

// queries 'span' css selector inside the result of '//html/body/div' xpath selector
const handle = await page.$('xpath=//html/body/div >> css=span');

// converted to 'css=div'
const handle = await page.$('div');

// converted to 'xpath=//html/body/div'
const handle = await page.$('//html/body/div');

// converted to 'text="foo"'
const handle = await page.$('"foo"');

// queries 'span' css selector inside the div handle
const handle = await divHandle.$('css=span');

Selector engines

css and css:light

css is a default engine - any malformed selector not starting with // nor starting and ending with a quote is assumed to be a css selector. For example, Playwright converts page.$('span > button') to page.$('css=span > button').

css:light engine is equivalent to Document.querySelector and behaves according to the CSS spec. However, it does not pierce shadow roots, which may be inconvenient when working with Shadow DOM and Web Components. For that reason, css engine pierces shadow roots. More specifically, every Descendant combinator pierces an arbitrary number of open shadow roots, including the implicit descendant combinator at the start of the selector.

css engine first searches for elements in the light dom in the iteration order, and then recursively inside open shadow roots in the iteration order. It does not search inside closed shadow roots or iframes.

Examples

<article>
  <div>In the light dom</div>
  <div slot='myslot'>In the light dom, but goes into the shadow slot</div>
  <open mode shadow root>
    <div class='in-the-shadow'>
      <span class='content'>
        In the shadow dom
        <open mode shadow root>
          <li id='target'>Deep in the shadow</li>
        </open mode shadow root>
      </span>
    </div>
    <slot name='myslot'></slot>
  </open mode shadow root>
</article>

Note that <open mode shadow root> is not an html element, but rather a shadow root created with element.attachShadow({mode: 'open'}).

  • Both "css=article div" and "css:light=article div" match the first <div>In the light dom</div>.
  • Both "css=article > div" and "css:light=article > div" match two div elements that are direct children of the article.
  • "css=article .in-the-shadow" matches the <div class='in-the-shadow'>, piercing the shadow root, while "css:light=article .in-the-shadow" does not match anything.
  • "css:light=article div > span" does not match anything, because both light-dom div elements do not contain a span.
  • "css=article div > span" matches the <span class='content'>, piercing the shadow root.
  • "css=article > .in-the-shadow" does not match anything, because <div class='in-the-shadow'> is not a direct child of article
  • "css:light=article > .in-the-shadow" does not match anything.
  • "css=article li#target" matches the <li id='target'>Deep in the shadow</li>, piercing two shadow roots.

xpath

XPath engine is equivalent to Document.evaluate. Example: xpath=//html/body.

Malformed selector starting with // or .. is assumed to be an xpath selector. For example, Playwright converts page.$('//html/body') to page.$('xpath=//html/body').

Note that xpath does not pierce shadow roots.

text and text:light

Text engine finds an element that contains a text node with the passed text. For example, page.click('text=Login') clicks on a login button, and page.waitForSelector('"lazy loaded text") waits for the "lazy loaded text" to appear in the page.

  • By default, the match is case-insensitive, ignores leading/trailing whitespace and searches for a substring. This means text= Login matches <button>Button loGIN (click me)</button>.
  • Text body can be escaped with single or double quotes for precise matching, insisting on exact match, including specified whitespace and case. This means text="Login " will only match <button>Login </button> with exactly one space after "Login". Quoted text follows the usual escaping rules, e.g. use \" to escape double quote in a double-quoted string: text="foo\"bar".
  • Text body can also be a JavaScript-like regex wrapped in / symbols. This means text=/^\\s*Login$/i will match <button> loGIN</button> with any number of spaces before "Login" and no spaces after.
  • Input elements of the type button and submit are rendered with their value as text, and text engine finds them. For example, text=Login matches <input type=button value="Login">.

Malformed selector starting and ending with a quote (either " or ') is assumed to be a text selector. For example, Playwright converts page.click('"Login"') to page.click('text="Login"').

text engine open pierces shadow roots similarly to css, while text:light does not. Text engine first searches for elements in the light dom in the iteration order, and then recursively inside open shadow roots in the iteration order. It does not search inside closed shadow roots or iframes.

id, data-testid, data-test-id, data-test and their :light counterparts

Attribute engines are selecting based on the corresponding attribute value. For example: data-test-id=foo is equivalent to css=[data-test-id="foo"], and id:light=foo is equivalent to css:light=[id="foo"].