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perf: add preload link for stylesheet #389

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merged 1 commit into from
Sep 28, 2020
Merged

perf: add preload link for stylesheet #389

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43 changes: 29 additions & 14 deletions src/app/core/utils/theme/theme.service.ts
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Original file line number Diff line number Diff line change
@@ -1,9 +1,10 @@
import { DOCUMENT } from '@angular/common';
import { Inject, Injectable, Renderer2, RendererFactory2 } from '@angular/core';
import { DOCUMENT, isPlatformServer } from '@angular/common';
import { Inject, Injectable, PLATFORM_ID, Renderer2, RendererFactory2, isDevMode } from '@angular/core';
import { Store, select } from '@ngrx/store';
import { distinctUntilChanged, filter } from 'rxjs/operators';
import { takeWhile } from 'rxjs/operators';

import { getTheme } from 'ish-core/store/core/configuration';
import { whenTruthy } from 'ish-core/utils/operators';

/**
* Service to add the configured/selected theme’s CSS file in the HTML’s head.
Expand All @@ -16,11 +17,13 @@ export class ThemeService {
private renderer: Renderer2;
private head: HTMLElement;
private themeLinks: HTMLElement[] = [];
private themePreloadLinks: HTMLElement[] = [];

constructor(
private rendererFactory: RendererFactory2,
@Inject(DOCUMENT) private document: Document,
private store: Store
private store: Store,
@Inject(PLATFORM_ID) private platformId: string
) {
this.head = this.document.head;
this.renderer = this.rendererFactory.createRenderer(undefined, undefined);
Expand All @@ -35,10 +38,10 @@ export class ThemeService {

init() {
this.store
.pipe(select(getTheme))
.pipe(
distinctUntilChanged(),
filter(x => !!x)
takeWhile(() => isPlatformServer(this.platformId) || isDevMode()),
select(getTheme),
whenTruthy()
)
.subscribe(async theme => {
const themeData = theme.split('|');
Expand Down Expand Up @@ -74,14 +77,26 @@ export class ThemeService {
}

private async loadCss(filename: string) {
const themePreloadLinkEl: HTMLElement = this.renderer.createElement('link');
this.renderer.setAttribute(themePreloadLinkEl, 'rel', 'preload');
this.renderer.setAttribute(themePreloadLinkEl, 'as', 'style');
this.renderer.setAttribute(themePreloadLinkEl, 'href', filename);
this.renderer.appendChild(this.head, themePreloadLinkEl);
this.themePreloadLinks = [...this.themePreloadLinks, themePreloadLinkEl];

// remove preload of previous theme
if (this.themePreloadLinks.length === 2) {
this.renderer.removeChild(this.head, this.themePreloadLinks.shift());
}

return new Promise(resolve => {
const linkEl: HTMLElement = this.renderer.createElement('link');
this.renderer.setAttribute(linkEl, 'rel', 'stylesheet');
this.renderer.setAttribute(linkEl, 'type', 'text/css');
this.renderer.setAttribute(linkEl, 'href', filename);
this.renderer.setProperty(linkEl, 'onload', resolve);
this.renderer.appendChild(this.head, linkEl);
this.themeLinks = [...this.themeLinks, linkEl];
const themeLinkEl: HTMLElement = this.renderer.createElement('link');
this.renderer.setAttribute(themeLinkEl, 'rel', 'stylesheet');
this.renderer.setAttribute(themeLinkEl, 'type', 'text/css');
this.renderer.setAttribute(themeLinkEl, 'href', filename);
this.renderer.setProperty(themeLinkEl, 'onload', resolve);
this.renderer.appendChild(this.head, themeLinkEl);
this.themeLinks = [...this.themeLinks, themeLinkEl];

// remove style of previous theme
if (this.themeLinks.length === 2) {
Expand Down