feat: pull validation into separate module

src/validators.js

@@ -0,0 +1,57 @@
+import {
+  MIN_SRCSET_WIDTH,
+  MAX_SRCSET_WIDTH,
+  DEFAULT_SRCSET_WIDTH_TOLERANCE
+} from './constants.js';
+
+export function validateAndDestructureOptions(options) {
+  if (options.widthTolerance !== undefined) {
+    validateWidthTolerance(options.widthTolerance);
+    var widthTolerance = options.widthTolerance;
+  } else {
+    var widthTolerance = DEFAULT_SRCSET_WIDTH_TOLERANCE;
+  }
+
+  var minWidth = options.minWidth === undefined ? MIN_SRCSET_WIDTH : options.minWidth;
+  var maxWidth = options.maxWidth === undefined ? MAX_SRCSET_WIDTH : options.maxWidth;
+
+  // Validate the range unless we're using defaults for both
+  if (minWidth != MIN_SRCSET_WIDTH || maxWidth != MAX_SRCSET_WIDTH) {
+    validateRange(minWidth, maxWidth);
+  }
+
+  return [widthTolerance, minWidth, maxWidth];
+}
+
+export function validateRange(min, max) {
+  if (!(Number.isInteger(min) && Number.isInteger(max)) || (min <= 0 || max <= 0) || (min > max)) {
+    throw new Error('The min and max srcset widths can only be passed positive Number values');
+  }
+}
+
+export function validateWidthTolerance(widthTolerance) {
+  if (typeof widthTolerance != 'number' || widthTolerance <= 0) {
+    throw new Error('The srcset widthTolerance argument can only be passed a positive scalar number');
+  }
+}
+
+export function validateWidths(customWidths) {
+  if (!Array.isArray(customWidths) || !customWidths.length) {
+    throw new Error('The widths argument can only be passed a valid non-empty array of integers');
+  } else {
+    var allPositiveIntegers = customWidths.every(
+      function (width) {
+        return Number.isInteger(width) && width > 0
+      }
+    );
+    if (!allPositiveIntegers) {
+      throw new Error('A custom widths argument can only contain positive integer values');
+    }
+  }
+}
+
+export function validateVariableQuality(disableVariableQuality) {
+  if (typeof disableVariableQuality != 'boolean') {
+    throw new Error('The disableVariableQuality argument can only be passed a Boolean value');
+  }
+}