flow like the river

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

@@ -0,0 +1,50 @@
+// @flow
+import PolishedError from '../internalHelpers/_errors'
+
+const cssVariableRegex = /--[\S]*/g
+
+/**
+ * Fetches the value of a passed CSS Variable in the :root scope, or otherwise returns a defaultValue if provided.
+ *
+ * @example
+ * // Styles as object usage
+ * const styles = {
+ *   'background': cssVar('--background-color'),
+ * }
+ *
+ * // styled-components usage
+ * const div = styled.div`
+ *   background: ${cssVar('--background-color')};
+ * `
+ *
+ * // CSS in JS Output
+ *
+ * element {
+ *   'background': 'red'
+ * }
+ */
+export default function cssVar(
+  cssVariable: string,
+  defaultValue?: string | number,
+): string | number {
+  if (!cssVariable || !cssVariable.match(cssVariableRegex)) {
+    throw new PolishedError(73)
+  }
+
+  let variableValue
+
+  /* eslint-disable */
+  /* istanbul ignore next */
+  if (typeof document !== 'undefined' && document.documentElement !== null) {
+    variableValue = getComputedStyle(document.documentElement).getPropertyValue(cssVariable)
+  }
+  /* eslint-enable */
+
+  if (variableValue) {
+    return variableValue.trim()
+  } else if (defaultValue) {
+    return defaultValue
+  }
+
+  throw new PolishedError(74)
+}