flow like the river

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

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+// @flow
+import getValueAndUnit from './getValueAndUnit'
+import PolishedError from '../internalHelpers/_errors'
+
+import type { ModularScaleRatio } from '../types/modularScaleRatio'
+
+export const ratioNames = {
+  minorSecond: 1.067,
+  majorSecond: 1.125,
+  minorThird: 1.2,
+  majorThird: 1.25,
+  perfectFourth: 1.333,
+  augFourth: 1.414,
+  perfectFifth: 1.5,
+  minorSixth: 1.6,
+  goldenSection: 1.618,
+  majorSixth: 1.667,
+  minorSeventh: 1.778,
+  majorSeventh: 1.875,
+  octave: 2,
+  majorTenth: 2.5,
+  majorEleventh: 2.667,
+  majorTwelfth: 3,
+  doubleOctave: 4,
+}
+
+function getRatio(ratioName: string): number {
+  return ratioNames[ratioName]
+}
+
+/**
+ * Establish consistent measurements and spacial relationships throughout your projects by incrementing an em or rem value up or down a defined scale. We provide a list of commonly used scales as pre-defined variables.
+ * @example
+ * // Styles as object usage
+ * const styles = {
+ *    // Increment two steps up the default scale
+ *   'fontSize': modularScale(2)
+ * }
+ *
+ * // styled-components usage
+ * const div = styled.div`
+ *    // Increment two steps up the default scale
+ *   fontSize: ${modularScale(2)}
+ * `
+ *
+ * // CSS in JS Output
+ *
+ * element {
+ *   'fontSize': '1.77689em'
+ * }
+ */
+export default function modularScale(
+  steps: number,
+  base?: number | string = '1em',
+  ratio?: ModularScaleRatio = 1.333,
+): string {
+  if (typeof steps !== 'number') {
+    throw new PolishedError(42)
+  }
+  if (typeof ratio === 'string' && !ratioNames[ratio]) {
+    throw new PolishedError(43)
+  }
+
+  const [realBase, unit] = typeof base === 'string' ? getValueAndUnit(base) : [base, '']
+  const realRatio = typeof ratio === 'string' ? getRatio(ratio) : ratio
+
+  if (typeof realBase === 'string') {
+    throw new PolishedError(44, base)
+  }
+
+  return `${realBase * realRatio ** steps}${unit || ''}`
+}