hack in truncation rounding mode support

src/view/com/util/numeric/format.ts

@@ -1,10 +1,43 @@
 import type {I18n} from '@lingui/core'
 
+const SUPPORTS_ROUNDING_MODE = detectRoundingModeSupport()
+
 export const formatCount = (i18n: I18n, num: number) => {
-  return i18n.number(num, {
+  const formattedNum = i18n.number(num, {
     notation: 'compact',
     maximumFractionDigits: 1,
     // `1,953` shouldn't be rounded up to 2k, it should be truncated.
     roundingMode: 'trunc',
   })
+  // some langagues like `jp` start truncating at different thresholds
+  // so skip if no truncation happens
+  if (SUPPORTS_ROUNDING_MODE || String(num) === formattedNum) {
+    return formattedNum
+  } else {
+    // HACK: janky workaround for formatjs not supporting roundingMode
+    // https://github.com/formatjs/formatjs/issues/4359
+    // TODO: remove when fixed by formatjs -sfn
+    //
+    // error is when the number is within 50 of the threshold to the next rounded value
+    // eg. 1050 is within 50 of 1100, so will incorrectly round to 1.1k. 1049 correctly goes to 1k
+    const isNearThreshould = num > 1000 && num % 100 >= 50
+    // applying `-((num % 100) - 49)` to the number will take it back down to beneath the threshold
+    const correctedNum = isNearThreshould ? num - ((num % 100) - 49) : num
+    return i18n.number(correctedNum, {
+      notation: 'compact',
+      maximumFractionDigits: 1,
+      roundingMode: 'trunc',
+    })
+  }
+}
+
+function detectRoundingModeSupport() {
+  const testNum = 1050
+  return (
+    Intl.NumberFormat('en-US', {
+      notation: 'compact',
+      maximumFractionDigits: 1,
+      roundingMode: 'trunc',
+    }).format(testNum) === '1k'
+  )
 }