Number of Wonderful Substrings LeetCode solution in JavaScript

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/**
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 * @param {string} word
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 * @return {number}
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 */
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var wonderfulSubstrings = function (word) {
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  let hashMap = {},
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    ans = 0,
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    binaryRepresentation = 0,
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    t,
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    pos,
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    number,
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    oneBitToggled;
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  hashMap[0] = 1;
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  for (let i = 0; i < word.length; i++) {
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    pos = word[i].charCodeAt(0) - "a".charCodeAt(0); //Let's use position 0 for a, 1 for b .... 9 for j
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    t = 1 << pos;
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    binaryRepresentation = binaryRepresentation ^ t; //Toggle the bit at pos in the current mask(pattern)
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    //This loop will check same binaryRepresentation and all the other binaryRepresentation with difference of 1 bit
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    for (let i = 0; i < 10; i++) {
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      //Check all the numbers by changing 1 position
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      number = 1 << i; //Change 1 bit at a time
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      oneBitToggled = binaryRepresentation ^ number;
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      if (hashMap[oneBitToggled] !== undefined) {
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        ans += hashMap[oneBitToggled];
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      }
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    }
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    if (hashMap[binaryRepresentation] === undefined) {
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      hashMap[binaryRepresentation] = 1;
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    } else {
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      ans += hashMap[binaryRepresentation];
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      hashMap[binaryRepresentation]++;
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    }
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  }
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  return ans;
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};