Guidelines on creating a recursive function in Typescript that calculates the common elements between multiple arrays of strings

I have a code snippet that calculates the intersection of multiple arrays of strings.

Play with Typescript here

export const findIntersection = (list1: string[], list2: string[], ...otherLists): string[] => {
  const result = [];

  for (let i = 0; i < list1.length; i++) {
      const item1 = list1[i];
      let found = false;
      
      for (let j = 0; j < list2.length && !found; j++) {
          found = item1 === list2[j];
      }
      if (found === true) {
          result.push(item1);
      }
  }

  if (otherLists.length) {
    return findIntersection(result, otherLists.shift(), ...otherLists);
  } else {
    return result;
  }
};

While this function works well in JS, I am facing some challenges while converting it to Typescript. Specifically, I'm struggling with typing the ...otherLists parameters.

The error message I'm receiving is as follows:

https://i.sstatic.net/vGS9B.png

arraystypescriptrecursionintersection

Answer №1

This is the way to write it out:

const findIntersection = (array1: string[], array2: string[], ...moreArrays: string[][]): string[] => {

  const commonElements = [];

  for (let i = 0; i < array1.length; i++) {
      const element1 = array1[i];
      let matchFound = false;
      
      for (let j = 0; j < array2.length && !matchFound; j++) {
          matchFound = element1 === array2[j];
      }
      
      if (matchFound) {
          commonElements.push(element1);
      }
  }

  const nextArray = moreArrays.shift();
  
  if (nextArray) {
    return findIntersection(commonElements, nextArray, ...moreArrays);
  }

  return commonElements;
};

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