feat: timezone name for opts.timezoneOffset and date argument, fixes #553

src/filters/date.ts

@@ -1,7 +1,7 @@
 import { toValue, stringify, isString, isNumber, TimezoneDate, LiquidDate, strftime } from '../util'
 import { FilterImpl } from '../template'
 
-export function date (this: FilterImpl, v: string | Date, format: string, timeZoneOffset?: number) {
+export function date (this: FilterImpl, v: string | Date, format: string, timezoneOffset?: number | string) {
   const opts = this.context.opts
   let date: LiquidDate
   v = toValue(v)
@@ -22,10 +22,10 @@ export function date (this: FilterImpl, v: string | Date, format: string, timeZo
     date = v
   }
   if (!isValidDate(date)) return v
-  if (timeZoneOffset !== undefined) {
-    date = new TimezoneDate(date, timeZoneOffset)
+  if (timezoneOffset !== undefined) {
+    date = new TimezoneDate(date, parseTimezoneOffset(date, timezoneOffset))
   } else if (opts.timezoneOffset !== undefined) {
-    date = new TimezoneDate(date, opts.timezoneOffset!)
+    date = new TimezoneDate(date, parseTimezoneOffset(date, opts.timezoneOffset))
   }
   return strftime(date, format)
 }
@@ -33,3 +33,13 @@ export function date (this: FilterImpl, v: string | Date, format: string, timeZo
 function isValidDate (date: any): date is Date {
   return (date instanceof Date || date instanceof TimezoneDate) && !isNaN(date.getTime())
 }
+
+/**
+ * need pass in a `date` because offset is dependent on whether DST is active
+ */
+function parseTimezoneOffset (date: Date, timeZone: string | number) {
+  if (isNumber(timeZone)) return timeZone
+  const utcDate = new Date(date.toLocaleString('en-US', { timeZone: 'UTC' }))
+  const tzDate = new Date(date.toLocaleString('en-US', { timeZone }))
+  return (utcDate.getTime() - tzDate.getTime()) / 6e4
+}

src/liquid-options.ts

@@ -35,8 +35,8 @@ export interface LiquidOptions {
   ownPropertyOnly?: boolean;
   /** Modifies the behavior of `strictVariables`. If set, a single undefined variable will *not* cause an exception in the context of the `if`/`elsif`/`unless` tag and the `default` filter. Instead, it will evaluate to `false` and `null`, respectively. Irrelevant if `strictVariables` is not set. Defaults to `false`. **/
   lenientIf?: boolean;
-  /** JavaScript timezoneOffset for `date` filter, default to local time. That means if you're in Australia (UTC+10), it'll default to -600 */
-  timezoneOffset?: number;
+  /** JavaScript timezone name or timezoneOffset for `date` filter, default to local time. That means if you're in Australia (UTC+10), it'll default to `-600` or `Australia/Lindeman` */
+  timezoneOffset?: number | string;
   /** Strip blank characters (including ` `, `\t`, and `\r`) from the right of tags (`{% %}`) until `\n` (inclusive). Defaults to `false`. */
   trimTagRight?: boolean;
   /** Similar to `trimTagRight`, whereas the `\n` is exclusive. Defaults to `false`. See Whitespace Control for details. */

test/integration/filters/date.ts

@@ -64,16 +64,29 @@ describe('filters/date', function () {
     it('should support timezone offset argument', function () {
       return test('{{ "1990-12-31T23:00:00Z" | date: "%Y-%m-%dT%H:%M:%S", 360}}', '1990-12-31T17:00:00')
     })
+    it('should support timezone name argument', function () {
+      return test('{{ "1990-12-31T23:00:00Z" | date: "%Y-%m-%dT%H:%M:%S", "Asia/Colombo" }}', '1991-01-01T04:30:00')
+    })
+    it('should support timezone name argument when DST is not active', function () {
+      return test('{{ "2021-01-01T23:00:00Z" | date: "%Y-%m-%dT%H:%M:%S", "America/New_York" }}', '2021-01-01T18:00:00')
+    })
+    it('should support timezone name argument when DST is active', function () {
+      return test('{{ "2021-06-01T23:00:00Z" | date: "%Y-%m-%dT%H:%M:%S", "America/New_York" }}', '2021-06-01T19:00:00')
+    })
     it('should offset date literal with timezone 00:00 specified', function () {
       return test('{{ "1990-12-31T23:00:00+00:00" | date: "%Y-%m-%dT%H:%M:%S"}}', '1990-12-31T17:00:00', undefined, opts)
     })
     it('should offset date literal with timezone -01:00 specified', function () {
       return test('{{ "1990-12-31T23:00:00-01:00" | date: "%Y-%m-%dT%H:%M:%S"}}', '1990-12-31T18:00:00', undefined, opts)
     })
-    it('should offset date from scope', function () {
+    it('should offset date from scope (timezone offset)', function () {
       const scope = { date: new Date('1990-12-31T23:00:00Z') }
       return test('{{ date | date: "%Y-%m-%dT%H:%M:%S"}}', scope, '1990-12-31T17:00:00', opts)
     })
+    it('should offset date from scope (timezone name)', function () {
+      const scope = { date: new Date('1990-12-31T23:00:00Z') }
+      return test('{{ date | date: "%Y-%m-%dT%H:%M:%S"}}', scope, '1990-12-31T17:00:00', { timezoneOffset: 'America/Merida' })
+    })
     it('should reflect timezoneOffset', function () {
       const scope = { date: new Date('1990-12-31T23:00:00Z') }
       return test('{{ date | date: "%z"}}', scope, '-0600', opts)