How to use 'count all permutations of a string' in JavaScript

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export default function StringPermutationsRecursive(string: string): number {
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  if (string.length === 1) {
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    permutations++;
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  }
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  const _string = string.split('');
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  for (let i = 0; i < _string.length; i++) {
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    StringPermutationsRecursive(
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      _string.filter((e: any, _i: number): boolean => _i !== i).join('')
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    );
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  }
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  return permutations;
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}

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function permutate(chars) { //recursive: generates the permutations
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  if(chars.length === 0) {
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    permutation_array.push(nextWord.join(''));
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  }
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  for (var i=0; i < chars.length; i++){
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    chars.push(chars.shift());  //rotate the characters
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    nextWord.push(chars[0]);    //use the first char in the array
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    permutate(chars.slice(1));  //Recurse: array-less-one-char
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    nextWord.pop();             //clear for nextWord (multiple pops)
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  }
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}