Add pageCount check, add getAdjacentIndexes

src/components/Carousel/Carousel.svelte

@@ -9,6 +9,7 @@
     addResizeEventListener,
     removeResizeEventListener
   } from '../../utils/event'
+  import { getAdjacentIndexes } from '../../utils/page'
 
   const directionFnDescription = {
     [NEXT]: showNextPage,
@@ -60,19 +61,14 @@
   let currentPageIndex = 0
   $: originalCurrentPageIndex = currentPageIndex - Number(infinite);
   let pagesCount = 0
-  $: originalPagesCount = Math.max(pagesCount - (infinite ? 2 : 0), 0) // without clones
+  $: originalPagesCount = Math.max(pagesCount - (infinite ? 2 : 0), 1) // without clones
   let pageWidth = 0
   let offset = 0
   let pageWindowElement
   let pagesElement
 
   // used for lazy loading images, preloaded only current, adjacent and cloanable images
-  $: loaded = [
+  $: loaded = getAdjacentIndexes(originalCurrentPageIndex, originalPagesCount)
-    ...new Set([
-      0, originalPagesCount-1,
-      originalCurrentPageIndex - 1, originalCurrentPageIndex, originalCurrentPageIndex + 1
-    ])
-  ].filter(index => index >= 0)
 
   function applyPageSizes() {
     const children = pagesElement.children

src/utils/page.js

@@ -1,8 +1,10 @@
 export function getNextPageIndexLimited(currentPageIndex, pagesCount) {
+  if (pagesCount < 1) throw new Error('pagesCount must be at least 1')
   return Math.min(Math.max(currentPageIndex + 1, 0), pagesCount - 1)
 }
 
 export function getNextPageIndexInfinte(currentPageIndex, pagesCount) {
+  if (pagesCount < 1) throw new Error('pagesCount must be at least 1')
   const newCurrentPageIndex = Math.max(currentPageIndex, 0) + 1
   return newCurrentPageIndex > pagesCount - 1 ? 0 : Math.max(newCurrentPageIndex, 0)
 }
@@ -12,10 +14,12 @@ export function getNextPageIndexFn(infinite) {
 }
 
 export function getPrevPageIndexLimited(currentPageIndex, pagesCount) {
+  if (pagesCount < 1) throw new Error('pagesCount must be at least 1')
   return Math.max(Math.min(currentPageIndex - 1, pagesCount - 1), 0)
 }
 
 export function getPrevPageIndexInfinte(currentPageIndex, pagesCount) {
+  if (pagesCount < 1) throw new Error('pagesCount must be at least 1')
   const newCurrentPageIndex = Math.min(currentPageIndex, pagesCount - 1) - 1
   return newCurrentPageIndex >= 0 ? Math.min(newCurrentPageIndex, pagesCount - 1) : pagesCount - 1
 }
@@ -25,5 +29,24 @@ export function getPrevPageIndexFn(infinite) {
 }
 
 export function getPageIndex(pageIndex, pagesCount) {
+  if (pagesCount < 1) throw new Error('pagesCount must be at least 1')
   return pageIndex < 0 ? 0 : Math.min(pageIndex, pagesCount - 1)
 }
+
+export function getAdjacentIndexes(pageIndex, pagesCount, infinite) {
+  if (pagesCount < 1) throw new Error('pagesCount must be at least 1')
+  const _pageIndex = Math.max(0, Math.min(pageIndex, pagesCount - 1))
+  let rangeStart = _pageIndex - 1;
+  let rangeEnd = _pageIndex + 1;
+  rangeStart = rangeStart < 0
+    ? infinite
+      ? pagesCount - 1
+      : 0
+    : rangeStart 
+  rangeEnd = rangeEnd > pagesCount - 1
+    ? infinite
+        ? 0
+        : pagesCount - 1
+    : rangeEnd
+  return [...new Set([rangeStart, rangeEnd, _pageIndex])].sort((a, b) => a - b)
+}

src/utils/page.test.js

@@ -3,8 +3,9 @@ import {
   getNextPageIndexInfinte,
   getPrevPageIndexLimited,
   getPrevPageIndexInfinte,
-  getPageIndex
+  getPageIndex,
-} from './page.js';
+  getAdjacentIndexes
+} from './page.js'
 
 describe('getNextPageIndexLimited', () => {
   it('returns next page index as expected', () => {
@@ -16,10 +17,17 @@ describe('getNextPageIndexLimited', () => {
       { currentPageIndex: 7, pagesCount: 3, expected: 2 },
     ]
     testCases.forEach(({ currentPageIndex, pagesCount, expected }) => {
-      expect(getNextPageIndexLimited(currentPageIndex, pagesCount)).toBe(expected);
+      expect(getNextPageIndexLimited(currentPageIndex, pagesCount)).toBe(expected)
-    });
+    })
-  });
+  })
-});
+  it('throws error if pagesCount is less than 1', () => {
+    const currentPageIndex = 5
+    const pagesCount = 0
+    expect(
+      () => getNextPageIndexLimited(currentPageIndex, pagesCount)
+    ).toThrowError('pagesCount must be at least 1')
+  })
+})
 
 describe('getNextPageIndexInfinte', () => {
   it('returns next page index as expected', () => {
@@ -31,10 +39,17 @@ describe('getNextPageIndexInfinte', () => {
       { currentPageIndex: 7, pagesCount: 3, expected: 0 },
     ]
     testCases.forEach(({ currentPageIndex, pagesCount, expected }) => {
-      expect(getNextPageIndexInfinte(currentPageIndex, pagesCount)).toBe(expected);
+      expect(getNextPageIndexInfinte(currentPageIndex, pagesCount)).toBe(expected)
-    });
+    })
-  });
+  })
-});
+  it('throws error if pagesCount is less than 1', () => {
+    const currentPageIndex = 5
+    const pagesCount = 0
+    expect(
+      () => getNextPageIndexInfinte(currentPageIndex, pagesCount)
+    ).toThrowError('pagesCount must be at least 1')
+  })
+})
 
 describe('getPrevPageIndexLimited', () => {
   it('returns prev page index as expected', () => {
@@ -46,10 +61,17 @@ describe('getPrevPageIndexLimited', () => {
       { currentPageIndex: 7, pagesCount: 3, expected: 2 },
     ]
     testCases.forEach(({ currentPageIndex, pagesCount, expected }) => {
-      expect(getPrevPageIndexLimited(currentPageIndex, pagesCount)).toBe(expected);
+      expect(getPrevPageIndexLimited(currentPageIndex, pagesCount)).toBe(expected)
-    });
+    })
-  });
+  })
-});
+  it('throws error if pagesCount is less than 1', () => {
+    const currentPageIndex = 5
+    const pagesCount = 0
+    expect(
+      () => getPrevPageIndexLimited(currentPageIndex, pagesCount)
+    ).toThrowError('pagesCount must be at least 1')
+  })
+})
 
 describe('getPrevPageIndexInfinte', () => {
   it('returns prev page index as expected', () => {
@@ -61,10 +83,17 @@ describe('getPrevPageIndexInfinte', () => {
       { currentPageIndex: 7, pagesCount: 3, expected: 1 },
     ]
     testCases.forEach(({ currentPageIndex, pagesCount, expected }) => {
-      expect(getPrevPageIndexInfinte(currentPageIndex, pagesCount)).toBe(expected);
+      expect(getPrevPageIndexInfinte(currentPageIndex, pagesCount)).toBe(expected)
-    });
+    })
-  });
+  })
-});
+  it('throws error if pagesCount is less than 1', () => {
+    const currentPageIndex = 5
+    const pagesCount = 0
+    expect(
+      () => getPrevPageIndexInfinte(currentPageIndex, pagesCount)
+    ).toThrowError('pagesCount must be at least 1')
+  })
+})
 
 describe('getPageIndex', () => {
   it('returns normalized page index as expected', () => {
@@ -76,7 +105,51 @@ describe('getPageIndex', () => {
       { pageIndex: 7, pagesCount: 3, expected: 2 },
     ]
     testCases.forEach(({ pageIndex, pagesCount, expected }) => {
-      expect(getPageIndex(pageIndex, pagesCount)).toBe(expected);
+      expect(getPageIndex(pageIndex, pagesCount)).toBe(expected)
-    });
+    })
-  });
+  })
-});
+  it('throws error if pagesCount is less than 1', () => {
+    const pageIndex = 5
+    const pagesCount = 0
+    expect(
+      () => getPageIndex(pageIndex, pagesCount)
+    ).toThrowError('pagesCount must be at least 1')
+  })
+})
+
+describe('getAdjacentIndexes', () => {
+  it('returns indexes as expected if infinite', () => {
+    const testCases = [
+      { pageIndex: 0, pagesCount: 1, expected: [0] },
+      { pageIndex: -5, pagesCount: 10, expected: [0, 1, 9] },
+      { pageIndex: 0, pagesCount: 10, expected: [0, 1, 9] },
+      { pageIndex: 5, pagesCount: 10, expected: [4, 5, 6] },
+      { pageIndex: 9, pagesCount: 10, expected: [0, 8, 9] },
+      { pageIndex: 15, pagesCount: 10, expected: [0, 8, 9] },
+    ]
+    testCases.forEach(({ pageIndex, pagesCount, expected }) => {
+      expect(getAdjacentIndexes(pageIndex, pagesCount, true)).toEqual(expected)
+    })
+  })
+  it('returns indexes as expected if not infinite', () => {
+    const testCases = [
+      { pageIndex: 0, pagesCount: 1, expected: [0] },
+      { pageIndex: -5, pagesCount: 10, expected: [0, 1] },
+      { pageIndex: 0, pagesCount: 10, expected: [0, 1] },
+      { pageIndex: 5, pagesCount: 10, expected: [4, 5, 6] },
+      { pageIndex: 9, pagesCount: 10, expected: [8, 9] },
+      { pageIndex: 15, pagesCount: 10, expected: [8, 9] },
+    ]
+    testCases.forEach(({ pageIndex, pagesCount, expected }) => {
+      expect(getAdjacentIndexes(pageIndex, pagesCount, false)).toEqual(expected)
+    })
+  })
+  it('throws error if pagesCount is less than 1', () => {
+    const pageIndex = 5
+    const pagesCount = 0
+    const infinite = true
+    expect(
+      () => getAdjacentIndexes(pageIndex, pagesCount, infinite)
+    ).toThrowError('pagesCount must be at least 1')
+  })
+})