export {}; // To get around: Cannot redeclare block-scoped variable 'mockLogger'.ts(2451)

/**
 * Calculate the sizes to be used for resizing the image based on the current size
 * @param width - the width of the original image
 * @return - an array of up to 4 elements representing the size
 * in each group
 */
const calcSizes = (width: number): ImageSize[] => {
  if (width < 1) {
    throw new Error(`Unexpected width less than 1: ${width}`);
  }

  const brackets = [{
    bracket: 100,
    name: 'thumb',
  }, {
    bracket: 500,
    name: 'sm',
  }, {
    bracket: 1000,
    name: 'md',
  }, {
    bracket: 1500,
    name: 'lg',
  }, {
    bracket: 2000,
    name: 'xl',
  }];

  return brackets.reduce(
    (acc: ImageSize[], { bracket, name }, index) => {
      let w;
      if (width > bracket) {
        w = bracket;
      } else if (index > 0 && width > brackets[index - 1].bracket && width <= bracket) {
        w = width;
      } else if (index === 0 && width <= bracket) {
        w = width;
      }
      if (w) {
        acc.push({ width: w, name });
      }
      return acc;
    }, [],
  );
};

module.exports = calcSizes;

export {}; // To get around: Cannot redeclare block-scoped variable 'mockLogger'.ts(2451)

/**
 * Calculate the sizes to be used for resizing the image based on the current size
 * @param {number} width - the width of the original image
 * @return {ImageSize[]} - an array of up to 4 elements representing the size
 * in each group
 */
function calcSizes(width: number): ImageSize[] {
  if (width < 1) {
    throw new Error(`Unexpected width less than 1: ${width}`);
  }

  const brackets = [{
    bracket: 100,
    name: 'thumb',
  }, {
    bracket: 500,
    name: 'sm',
  }, {
    bracket: 1000,
    name: 'md',
  }, {
    bracket: 1500,
    name: 'lg',
  }, {
    bracket: 2000,
    name: 'xl',
  }];

  return brackets.reduce(
    (acc: ImageSize[], { bracket, name }, index) => {
      let w;
      if (width > bracket) {
        w = bracket;
      } else if (index > 0 && width > brackets[index - 1].bracket && width <= bracket) {
        w = width;
      } else if (index === 0 && width <= bracket) {
        w = width;
      }
      if (w) {
        acc.push({ width: w, name });
      }
      return acc;
    }, [],
  );
}

module.exports = calcSizes;

--- 
+++ 
@@ -2,11 +2,11 @@
 
 /**
  * Calculate the sizes to be used for resizing the image based on the current size
- * @param {number} width - the width of the original image
- * @return {ImageSize[]} - an array of up to 4 elements representing the size
+ * @param width - the width of the original image
+ * @return - an array of up to 4 elements representing the size
  * in each group
  */
-function calcSizes(width: number): ImageSize[] {
+const calcSizes = (width: number): ImageSize[] => {
   if (width < 1) {
     throw new Error(`Unexpected width less than 1: ${width}`);
   }
@@ -44,6 +44,6 @@
       return acc;
     }, [],
   );
-}
+};
 
 module.exports = calcSizes;
Change calcSizes from function to arrow function
