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Add a slimDOM option to strip out unnecessary parts of the DOM (#36)

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* Add a `slimDOM` option to strip out unnecessary parts of the DOM in terms of replay

 - <script> tags in the <head> take up unnecessary storage space and are often injected semi randomly to become a source of unnecessary variation between recordings of the same thing
 - comment tags can be stripped out without affecting display
 - future: this option could also turn on more aggressive stripping, e.g. elements that are hidden by CSS (assuming we can handle them becoming visible after mutation events)

* Mark nodes ignored due to slimDOM option, so that they can also be ignored by the mutation observer in rrweb

* Introducing the `ignored` attribute violates the `serializedNodeWithId` type

* slimDOM: Strip out whitespace nodes from <head> element as they have no effect but take up space

 - these would otherwise have to be merged after <script> elements are removed; for statcounter usecase, removing
   <script> elements is no good if there is still a trace of their presence due to the white space (and hence a variant <head> node is still produced)
 - I explored a more radical stripping of all white space nodes, but there is a problem if parent node is <pre> or otherwise rendered with `white-space: pre` and similar.
   detecting applied styles with getComputedStyle would be very expensive (I haven't measured it though)

* Export IGNORED_NODE as a constant instead of relying on the hard-to-grok `-2`

* Remove <link rel=preload as=script> which are similarly as useless as <script> tags

* Make slimDOM configurable with the expecations that `slimDOMOptions: true` will only enable non-destructive options (so not all options may be turned on)

* Expand slimDOM to add options to remove more elements from the <head> that should not be necessary in the replayer context
This commit is contained in:
Eoghan Murray
2026-04-01 12:00:00 +08:00
committed by GitHub
parent d8ba0cc8e2
commit 71b6e683c0
3 changed files with 139 additions and 0 deletions
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2
src/index.ts
View File

@@ -2,6 +2,7 @@ import snapshot, {
serializeNodeWithId,
transformAttribute,
visitSnapshot,
IGNORED_NODE,
} from './snapshot';
import rebuild, { buildNodeWithSN, addHoverClass } from './rebuild';
export * from './types';
@@ -14,4 +15,5 @@ export {
addHoverClass,
transformAttribute,
visitSnapshot,
IGNORED_NODE,
};

124
src/snapshot.ts
View File

@@ -6,11 +6,14 @@ import {
INode,
idNodeMap,
MaskInputOptions,
SlimDOMOptions,
} from './types';
let _id = 1;
const tagNameRegex = RegExp('[^a-z1-6-_]');
export const IGNORED_NODE = -2;
function genId(): number {
return _id++;
}
@@ -323,6 +326,83 @@ function serializeNode(
}
}
function lowerIfExists(maybeAttr : string | number | boolean) : string {
if (maybeAttr === undefined) {
return '';
} else {
return (maybeAttr as string).toLowerCase();
}
}
function slimDOMExcluded(sn: serializedNode, slimDOMOptions: SlimDOMOptions): boolean {
if (slimDOMOptions.comment && sn.type === NodeType.Comment) {
// TODO: convert IE conditional comments to real nodes
return true;
} else if (sn.type === NodeType.Element) {
if (slimDOMOptions.script &&
(sn.tagName === 'script' ||
(sn.tagName === 'link' && sn.attributes.rel === 'preload' && sn.attributes['as'] === 'script')
)) {
return true;
} else if (slimDOMOptions.headFavicon && (
(sn.tagName === 'link' && sn.attributes.rel === 'shortcut icon')
|| (sn.tagName === 'meta' && (
lowerIfExists(sn.attributes['name']).match(/^msapplication-tile(image|color)$/)
|| lowerIfExists(sn.attributes['name']) === 'application-name'
|| lowerIfExists(sn.attributes['rel']) === 'icon'
|| lowerIfExists(sn.attributes['rel']) === 'apple-touch-icon'
|| lowerIfExists(sn.attributes['rel']) === 'shortcut icon'
)))) {
return true;
} else if (sn.tagName === 'meta') {
if (slimDOMOptions.headMetaDescKeywords && (
lowerIfExists(sn.attributes['name']).match(/^description|keywords$/)
)) {
return true;
} else if (slimDOMOptions.headMetaSocial && (
lowerIfExists(sn.attributes['property']).match(/^(og|twitter|fb):/) // og = opengraph (facebook)
|| lowerIfExists(sn.attributes['name']).match(/^(og|twitter):/)
|| lowerIfExists(sn.attributes['name']) === 'pinterest'
)) {
return true;
} else if (slimDOMOptions.headMetaRobots && (
lowerIfExists(sn.attributes['name']) === 'robots'
|| lowerIfExists(sn.attributes['name']) === 'googlebot'
|| lowerIfExists(sn.attributes['name']) === 'bingbot'
)) {
return true;
} else if (slimDOMOptions.headMetaHttpEquiv && (
sn.attributes['http-equiv'] !== undefined
)) {
// e.g. X-UA-Compatible, Content-Type, Content-Language,
// cache-control, X-Translated-By
return true;
} else if (slimDOMOptions.headMetaAuthorship && (
lowerIfExists(sn.attributes['name']) === 'author'
|| lowerIfExists(sn.attributes['name']) === 'generator'
|| lowerIfExists(sn.attributes['name']) === 'framework'
|| lowerIfExists(sn.attributes['name']) === 'publisher'
|| lowerIfExists(sn.attributes['name']) === 'progid'
|| lowerIfExists(sn.attributes['property']).match(/^article:/)
|| lowerIfExists(sn.attributes['property']).match(/^product:/)
)) {
return true;
} else if (slimDOMOptions.headMetaVerification && (
lowerIfExists(sn.attributes['name']) === 'google-site-verification'
|| lowerIfExists(sn.attributes['name']) === 'yandex-verification'
|| lowerIfExists(sn.attributes['name']) === 'csrf-token'
|| lowerIfExists(sn.attributes['name']) === 'p:domain_verify'
|| lowerIfExists(sn.attributes['name']) === 'verify-v1'
|| lowerIfExists(sn.attributes['name']) === 'verification'
|| lowerIfExists(sn.attributes['name']) === 'shopify-checkout-api-token'
)) {
return true;
}
}
}
return false;
}
export function serializeNodeWithId(
n: Node | INode,
doc: Document,
@@ -331,7 +411,9 @@ export function serializeNodeWithId(
skipChild = false,
inlineStylesheet = true,
maskInputOptions?: MaskInputOptions,
slimDOMOptions: SlimDOMOptions = {},
recordCanvas?: boolean,
preserveWhiteSpace = true,
): serializedNodeWithId | null {
const _serializedNode = serializeNode(
n,
@@ -346,15 +428,26 @@ export function serializeNodeWithId(
console.warn(n, 'not serialized');
return null;
}
let id;
// Try to reuse the previous id
if ('__sn' in n) {
id = n.__sn.id;
} else if (slimDOMExcluded(_serializedNode, slimDOMOptions) ||
(!preserveWhiteSpace &&
_serializedNode.type === NodeType.Text &&
!_serializedNode.isStyle &&
!_serializedNode.textContent.replace(/^\s+|\s+$/gm,'').length
)) {
id = IGNORED_NODE;
} else {
id = genId();
}
const serializedNode = Object.assign(_serializedNode, { id });
(n as INode).__sn = serializedNode;
if (id === IGNORED_NODE) {
return null; // slimDOM
}
map[id] = n as INode;
let recordChild = !skipChild;
if (serializedNode.type === NodeType.Element) {
@@ -367,6 +460,14 @@ export function serializeNodeWithId(
serializedNode.type === NodeType.Element) &&
recordChild
) {
if (
(slimDOMOptions.headWhitespace &&
_serializedNode.type === NodeType.Element &&
_serializedNode.tagName == 'head')
// would impede performance: || getComputedStyle(n)['white-space'] === 'normal'
) {
preserveWhiteSpace = false;
}
for (const childN of Array.from(n.childNodes)) {
const serializedChildNode = serializeNodeWithId(
childN,
@@ -376,7 +477,9 @@ export function serializeNodeWithId(
skipChild,
inlineStylesheet,
maskInputOptions,
slimDOMOptions,
recordCanvas,
preserveWhiteSpace,
);
if (serializedChildNode) {
serializedNode.childNodes.push(serializedChildNode);
@@ -391,6 +494,7 @@ function snapshot(
blockClass: string | RegExp = 'rr-block',
inlineStylesheet = true,
maskAllInputsOrOptions: boolean | MaskInputOptions,
slimDOMSensibleOrOptions: boolean | SlimDOMOptions,
recordCanvas?: boolean,
): [serializedNodeWithId | null, idNodeMap] {
const idNodeMap: idNodeMap = {};
@@ -416,6 +520,25 @@ function snapshot(
: maskAllInputsOrOptions === false
? {}
: maskAllInputsOrOptions;
const slimDOMOptions: SlimDOMOptions =
(slimDOMSensibleOrOptions === true ||
slimDOMSensibleOrOptions === 'all')
// if true: set of sensible options that should not throw away any information
? {
script: true,
comment: true,
headFavicon: true,
headWhitespace: true,
headMetaDescKeywords: slimDOMSensibleOrOptions === 'all', // destructive
headMetaSocial: true,
headMetaRobots: true,
headMetaHttpEquiv: true,
headMetaAuthorship: true,
headMetaVerification: true,
}
: slimDOMSensibleOrOptions === false
? {}
: slimDOMSensibleOrOptions;
return [
serializeNodeWithId(
n,
@@ -425,6 +548,7 @@ function snapshot(
false,
inlineStylesheet,
maskInputOptions,
slimDOMOptions,
recordCanvas,
),
idNodeMap,

13
src/types.ts
View File

@@ -87,3 +87,16 @@ export type MaskInputOptions = Partial<{
textarea: boolean;
select: boolean;
}>;
export type SlimDOMOptions = Partial<{
script: boolean;
comment: boolean;
headFavicon: boolean;
headWhitespace: boolean;
headMetaDescKeywords: boolean;
headMetaSocial: boolean;
headMetaRobots: boolean;
headMetaHttpEquiv: boolean;
headMetaAuthorship: boolean;
headMetaVerification: boolean;
}>;