NSString from NSDate and vice versa

NSDate+FormattedString.h

#import <Foundation/Foundation.h>

@interface NSDate (FormattedString)
- (NSString *)mi_dateStringWithStyle:(NSDateFormatterStyle)style 
                        timeStyle:(NSDateFormatterStyle)timeStyle;
- (NSString *)mi_dateStringWithFormat:(NSString *)format;
- (NSString *)mi_isoDateString;
- (NSString *)mi_ecma262DateString;
@end

NSDate+FormattedString.m

#import "NSDate+FormattedString.h"

@implementation NSDate (FormattedStrings)
- (NSString *)mi_dateStringWithStyle:(NSDateFormatterStyle)style 
                        timeStyle:(NSDateFormatterStyle)timeStyle {
    static NSDateFormatter *dateFormatter = nil;
    if(dateFormatter == nil)
    {
        dateFormatter = [[NSDateFormatter alloc] init];
    }
    [dateFormatter setFormatterBehavior:NSDateFormatterBehavior10_4];
    [dateFormatter setDateStyle:style];
    [dateFormatter setTimeStyle:timeStyle];
    return [dateFormatter stringFromDate:self];
}

- (NSString *)mi_dateStringWithFormat:(NSString *)format
{
    static NSDateFormatter *dateFormatter = nil;
    if(dateFormatter == nil)
    {
        dateFormatter = [[NSDateFormatter alloc] init];
    }
    [dateFormatter setFormatterBehavior:NSDateFormatterBehavior10_4];
    [dateFormatter setDateFormat:format];
    return [dateFormatter stringFromDate:self];
}

- (NSString *)mi_isoDateString
{
    return [self dateStringWithFormat:@"yyyy-MM-dd HH:mm:ss ZZZ"];
}

- (NSString *)mi_ecma262DateString
{
    return [self dateStringWithFormat:@"yyyy-MM-dd'T'HH:mm:ss.SSSZ"]; //YYYY-MM-DDThh:mm[:ss[.uuuuuu]][+HHMM|-HHMM|Z]
}

@end

NSString+DateFormatter.h

#import <Foundation/Foundation.h>

@interface NSString (DateFormatter)
/**
 *  converts the string to date using `format`
 *
 *  @param format string format
 *
 *  @return the date corresponding to the string
 */
- (NSDate *)mi_dateWithFromat:(NSString *)format;

- (NSDate *)mi_dateWithISOString;

- (NSDate *)mi_dateWithECMA262String;
@end

NSString+DateFormatter.m

#import "NSString+DateFormatter.h"


@implementation NSString (DateForamtter)
- (NSDate *)mi_dateWithFromat:(NSString *)format {
    static NSDateFormatter *dateFormatter = nil;
    if(dateFormatter == nil)
    {
        dateFormatter = [[NSDateFormatter alloc] init];
    }
    [dateFormatter setFormatterBehavior:NSDateFormatterBehavior10_4];
    [dateFormatter setDateFormat:format];
    return [dateFormatter dateFromString:self];
}

- (NSDate *)mi_dateWithISOString
{
    static NSDateFormatter *dateFormatter = nil;
    if(dateFormatter == nil)
    {
        dateFormatter = [[NSDateFormatter alloc] init];
    }
    [dateFormatter setFormatterBehavior:NSDateFormatterBehavior10_4];
    [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss ZZZ"];
    return [dateFormatter dateFromString:self];
}

- (NSDate *)mi_dateWithECMA262String
{
    NSDate *d = [self dateWithFromat:@"YYYY-MM-dd'T'HH:mm:ss.SSSZ"];
    if(d == nil)
    {
        d = [self dateWithFromat:@"YYYY-MM-dd'T'HH:mm:ssZ"];
    }
    
    if(d == nil)
    {
        d = [self dateWithFromat:@"yyyy-MM-dd"];
    }
    return d;
}

@end