flow like the river

VISUALIZACION/node_modules/polished/lib/helpers/remToPx.js.flow

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+// @flow
+import getValueAndUnit from './getValueAndUnit'
+import PolishedError from '../internalHelpers/_errors'
+
+const defaultFontSize = 16
+
+function convertBase(base: string | number): number {
+  const deconstructedValue = getValueAndUnit(base)
+  if (deconstructedValue[1] === 'px') {
+    return parseFloat(base)
+  }
+
+  if (deconstructedValue[1] === '%') {
+    return (parseFloat(base) / 100) * defaultFontSize
+  }
+
+  throw new PolishedError(78, deconstructedValue[1])
+}
+
+function getBaseFromDoc(): number {
+  /* eslint-disable */
+  /* istanbul ignore next */
+  if (typeof document !== 'undefined' && document.documentElement !== null) {
+    const rootFontSize = getComputedStyle(document.documentElement).fontSize
+    return rootFontSize ? convertBase(rootFontSize) : defaultFontSize
+  }
+  /* eslint-enable */
+  /* istanbul ignore next */
+  return defaultFontSize
+}
+
+/**
+ * Convert rem values to px. By default, the base value is pulled from the font-size property on the root element (if it is set in % or px). It defaults to 16px if not found on the root. You can also override the base value by providing your own base in % or px.
+ * @example
+ * // Styles as object usage
+ * const styles = {
+ *   'height': remToPx('1.6rem')
+ *   'height': remToPx('1.6rem', '10px')
+ * }
+ *
+ * // styled-components usage
+ * const div = styled.div`
+ *   height: ${remToPx('1.6rem')}
+ *   height: ${remToPx('1.6rem', '10px')}
+ * `
+ *
+ * // CSS in JS Output
+ *
+ * element {
+ *   'height': '25.6px',
+ *   'height': '16px',
+ * }
+ */
+export default function remToPx(value: string | number, base?: string | number): string {
+  const deconstructedValue = getValueAndUnit(value)
+
+  if (deconstructedValue[1] !== 'rem' && deconstructedValue[1] !== '') {
+    throw new PolishedError(77, deconstructedValue[1])
+  }
+
+  const newBase = base ? convertBase(base) : getBaseFromDoc()
+  return `${deconstructedValue[0] * newBase}px`
+}