Directly check for existence of gtag script tag #2339
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Feiyang1
reviewed
Nov 7, 2019
| expect(getOrCreateDataLayer('dataLayer')).to.deep.equal([]); | ||
| }); | ||
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| it('getOrCreateDataLayer is able to correctly identify an existing data layer', () => { |
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This test is exactly the same as the one above. Do you mean to test something else?
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Oops, yes, changed.
packages/analytics/src/helpers.ts
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| @@ -80,7 +77,7 @@ export function insertScriptTag(dataLayerName: string): void { | |||
| export function getOrCreateDataLayer(dataLayerName: string): DataLayer { | |||
| // Check for existing dataLayer and create if needed. | |||
| let dataLayer: DataLayer = []; | |||
| if (hasDataLayer(dataLayerName)) { | |||
| if (Array.isArray(window[dataLayerName])) { | |||
| dataLayer = window[dataLayerName] as DataLayer; | |||
| } else { | |||
| dataLayer = window[dataLayerName] = []; | |||
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Since dataLayer is already initialized with [], you can avoid one memory allocation by window[dataLayerName] = dataLayer
| */ | ||
| export function findGtagScriptOnPage(): HTMLScriptElement | null { | ||
| const scriptTags = window.document.getElementsByTagName('script'); | ||
| for (const tag of Object.values(scriptTags)) { |
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You an iterate directly on scriptTags - for (const tag of scriptTags)
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Confirmed we cannot do this without downlevelIteration and adding dom.iterable TS lib, which we agreed adds unnecessary bloat to the analytics package.
Feiyang1
approved these changes
Nov 7, 2019
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We previously checked for pre-existence of a gtag script by looking for
window.dataLayer. This is not an accurate check in some cases, such as if the user is using Google Tag Manager on the page, which creates awindow.dataLayerbut does not insert a script tag to downloadgtag.js.This change directly checks the DOM for existence of such a script tag, and we will insert it if not found.