An Angular pipe for converting a date string into a time ago

time-elapsed.pipe.ts

// Angular
import { Pipe, PipeTransform, OnDestroy, ChangeDetectorRef, NgZone } from '@angular/core';

/**
 * https://github.com/AndrewPoyntz/time-ago-pipe
 * An Angular pipe for converting a date string into a time ago
 *
 * Example :
 * <span>Last {{ date | kTimeElapsed}} ago</span>
 */
@Pipe({
    name: 'kTimeElapsed'
})
export class TimeElapsedPipe implements PipeTransform, OnDestroy {
    private _timer: number;

    /**
     * Pipe Constructor
     *
     * @param changeDetectorRef: ChangeDetectorRef
     * @param ngZone: NgZone
     */
    constructor(
        private changeDetectorRef: ChangeDetectorRef,
        private ngZone: NgZone
    ) {}

    /**
     * @ Lifecycle sequences => https://angular.io/guide/lifecycle-hooks
     */
    ngOnDestroy(): void {
        this.removeTimer();
    }

    /**
     * Transform
     *
     * @param value: string time
     * @param textBefore: string - text Before calculated time
     * @param textAfter: string - text after calculated time
     */
    transform(value: string, textBefore?: string, textAfter?: string): string {
        this.removeTimer();
        let timeElapsed: string = '';

        if (!value) {
            return timeElapsed;
        }

        const d = new Date(value);
        const now = new Date();
        const seconds = Math.round(Math.abs((now.getTime() - d.getTime()) / 1000));
        const timeToUpdate = this.getSecondsUntilUpdate(seconds) * 1000;
        this._timer = this.ngZone.runOutsideAngular(() => {
            if (typeof window !== 'undefined') {
                return window.setTimeout(() => {
                    this.ngZone.run(() =>
                        this.changeDetectorRef.markForCheck()
                    );
                }, timeToUpdate);
            }
            return null;
        });

        const minutes = Math.round(Math.abs(seconds / 60));
        const hours = Math.round(Math.abs(minutes / 60));
        const days = Math.round(Math.abs(hours / 24));
        const months = Math.round(Math.abs(days / 30.416));
        const years = Math.round(Math.abs(days / 365));

        if (seconds <= 45) {
            timeElapsed = 'just now';
        } else if (seconds <= 90) {
            timeElapsed = `${textBefore} 1 min ${textAfter}`;
        } else if (minutes <= 45) {
            timeElapsed = `${textBefore} ${minutes} mins ${textAfter}`;
        } else if (minutes <= 90) {
            timeElapsed = `${textBefore} 1 hr ${textAfter}`;
        } else if (hours <= 22) {
            timeElapsed = `${textBefore} ${hours} hrs ${textAfter}`;
        } else if (hours <= 36) {
            timeElapsed = `${textBefore} 1 day ${textAfter}`;
        } else if (days <= 25) {
            timeElapsed = `${textBefore} ${days} days ${textAfter}`;
        } else if (days <= 45) {
            timeElapsed = `${textBefore} 1 month ${textAfter}`;
        } else if (days <= 345) {
            timeElapsed = `${textBefore} ${months} months ${textAfter}`;
        } else if (days <= 545) {
            timeElapsed = `${textBefore} 1 year ${textAfter}`;
        } else {
            // (days > 545)
            timeElapsed = `${textBefore} ${years} years ${textAfter}`;
        }

        return this.capitalizeFirstLetter(timeElapsed);
    }

    /**
     * Remove _timer
     */
    private removeTimer(): void {
        if (this._timer) {
            window.clearTimeout(this._timer);
            this._timer = null;
        }
    }

    /**
     * Returns Seconds Until Update
     * @param seconds: number
     */
    private getSecondsUntilUpdate(seconds: number): number {
        const min = 60;
        const hr = min * 60;
        const day = hr * 24;
        if (seconds < min) {
            // less than 1 min, update ever 2 secs
            return 2;
        } else if (seconds < hr) {
            // less than an hour, update every 30 secs
            return 30;
        } else if (seconds < day) {
            // less then a day, update every 5 mins
            return 300;
        } else {
            // update every hour
            return 3600;
        }
    }
    
    
    private capitalizeFirstLetter(str: string): string {
        return str.charAt(0).toUpperCase() + str.slice(1);
    }
}