1 files changed, 33 insertions, 0 deletions
diff --git a/date-fns/src/_lib/startOfUTCWeek/index.js b/date-fns/src/_lib/startOfUTCWeek/index.js
new file mode 100644
index 0000000..fb5db75
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+++ b/date-fns/src/_lib/startOfUTCWeek/index.js
@@ -0,0 +1,33 @@
+import toInteger from '../toInteger/index'
+import toDate from '../../toDate/index'
+import requiredArgs from '../requiredArgs/index'
+
+// This function will be a part of public API when UTC function will be implemented.
+// See issue: https://github.com/date-fns/date-fns/issues/376
+export default function startOfUTCWeek(dirtyDate, dirtyOptions) {
+  requiredArgs(1, arguments)
+
+  var options = dirtyOptions || {}
+  var locale = options.locale
+  var localeWeekStartsOn =
+    locale && locale.options && locale.options.weekStartsOn
+  var defaultWeekStartsOn =
+    localeWeekStartsOn == null ? 0 : toInteger(localeWeekStartsOn)
+  var weekStartsOn =
+    options.weekStartsOn == null
+      ? defaultWeekStartsOn
+      : toInteger(options.weekStartsOn)
+
+  // Test if weekStartsOn is between 0 and 6 _and_ is not NaN
+  if (!(weekStartsOn >= 0 && weekStartsOn <= 6)) {
+    throw new RangeError('weekStartsOn must be between 0 and 6 inclusively')
+  }
+
+  var date = toDate(dirtyDate)
+  var day = date.getUTCDay()
+  var diff = (day < weekStartsOn ? 7 : 0) + day - weekStartsOn
+
+  date.setUTCDate(date.getUTCDate() - diff)
+  date.setUTCHours(0, 0, 0, 0)
+  return date
+}