Media Observer

What

This is basically the same Media Observer you can find into @angular/flex, with an additional method like the one you can find in @angular/cdk, in order to check custom media queries (such as portrait, or simply media queries not declared initially. The difference is that this is for javascript/typescript use (e.g. React maybe).

Why

I think that it's very useful to avoid listening multiple times for window resizes and centralize responsive behaviours (when CSS media queries aren't enough, of course).

How

In Angular you can inject the instance, so this version is set for working as a singleton. You won't need to create an instance calling new MediaObserverService() (although in non-typescript projects you may be able to do so). You can access the singleton instance using the static getter INSTANCE.

E.g.:

import {MediaObserverService} from "media-observer";

const mosInstance = MediaObserverService.INSTANCE;

The MediaObserverService will provide mediaQuery activations notifications for all registered breakpoints.

This service is essentially an Observable that exposes both features to subscribe to mediaQuery changes and a validator method .isActive() to test if a mediaQuery (or alias) is currently active.

Only mediaChange activations (not deactivations) are announced by the ObservableMedia!

---

API Summary

The class MediaObserverService service has three (3) APIs:

• asObservable(): Observable<MediaChange>
• isActive(query: string | string[]): boolean
• isMatched(query: string | string[]): boolean

---

asObservable

This notifies when the current breakpoint is changed and returns the list of all active media queries

mosInstance.asObservable()
.pipe(filter((changes: MediaChanges) => changes[0].mqAlias === BreakpointAliases.xs))
.subscribe(() => this.loadMobileContent());

isActive

This allows to check if one of the registered media queries is active, by alias or by media query

 if (mosInstance.isActive(BreakpointAliases.xs)) {
    this.loadMobileContent();
}

isMatched

This is basically identical to isActive, except it allows to check any media query, even if not registered. So you can use the method to evaluate one or more media queries against the current viewport size.

const PRINT_MOBILE = 'print and (max-width: 599px)';
if (mosInstance.isMatched(PRINT_MOBILE)) {
    this.doSomePrintStuff();
}

Customizing breakpoints

Default breakpoints and aliases are accessible through the following vars:

• DEFAULT_BREAKPOINT_WIDTHS: links aliases and media query widths
• DEFAULT_BREAKPOINTS: the default breakpoint items that will be watched as soon as MediaObserverService is instantiated
• BreakpointAliases: contains all the standard aliases (you can use your own if you prefer)

To change the default breakpoints and use your own, just call the static method MediaObserverService.setBreakpoints, passing the list (an Array of BreakPoint) of your breakpoints, ** before** anyone calls MediaObserverService.INSTANCE.

To change the breakpoints after initialization you can call MediaObserverService.INSTANCE.destroy, which will destroy the active instance.

Default breakpoints

export interface BreakPoint {
    alias: BreakpointAliases | string;
    mediaQuery: string;
    overlapping?: boolean;  // Does this range overlap with any other ranges
    priority?: number;      // determine order of activation reporting: higher is last reported
    suffix?: string;
}

// Generated
export const DEFAULT_BREAKPOINTS: BreakPoint[] = [
    {
        alias: BreakpointAliases.xs,
        mediaQuery: "screen and (min-width: 0px) and (max-width: 599.98px)",
        priority: 1000
    },
    {
        alias: BreakpointAliases.sm,
        mediaQuery: "screen and (min-width: 600px) and (max-width: 959.98px)",
        priority: 900
    },
    {
        alias: BreakpointAliases.md,
        mediaQuery: "screen and (min-width: 960px) and (max-width: 1279.98px)",
        priority: 800
    },
    {
        alias: BreakpointAliases.lg,
        mediaQuery: "screen and (min-width: 1280px) and (max-width: 1919.98px)",
        priority: 700
    },
    {
        alias: BreakpointAliases.xl,
        mediaQuery: "screen and (min-width: 1920px) and (max-width: 4999.98px)",
        priority: 600
    },
    {
        alias: BreakpointAliases["lt-sm"],
        overlapping: true,
        mediaQuery: "screen and (max-width: 599.98px)",
        priority: 950
    },
    {
        alias: BreakpointAliases["lt-md"],
        overlapping: true,
        mediaQuery: "screen and (max-width: 959.98px)",
        priority: 850
    },
    {
        alias: BreakpointAliases["lt-lg"],
        overlapping: true,
        mediaQuery: "screen and (max-width: 1279.98px)",
        priority: 750
    },
    {
        alias: BreakpointAliases["lt-xl"],
        overlapping: true,
        priority: 650,
        mediaQuery: "screen and (max-width: 1919.98px)",
    },
    {
        alias: BreakpointAliases["gt-xs"],
        overlapping: true,
        mediaQuery: "screen and (min-width: 600px)",
        priority: -950
    },
    {
        alias: BreakpointAliases["gt-sm"],
        overlapping: true,
        mediaQuery: "screen and (min-width: 960px)",
        priority: -850
    }, {
        alias: BreakpointAliases["gt-md"],
        overlapping: true,
        mediaQuery: "screen and (min-width: 1280px)",
        priority: -750
    },
    {
        alias: BreakpointAliases["gt-lg"],
        overlapping: true,
        mediaQuery: "screen and (min-width: 1920px)",
        priority: -650
    }
];