Number of Provinces LeetCode solution in JavaScript

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function DisjointSet(size) {
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  this.root = [];
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  this.rank = [];
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  this.size = size;
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  for (let i = 0; i < size; i++) {
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    this.root.push(i);
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    this.rank.push(1);
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  }
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  this.find = function (x) {
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    if (x === this.root[x]) {
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      return x;
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    }
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    this.root[x] = this.find(this.root[x]);
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    return this.root[x];
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  };
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  this.union = function (x, y) {
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    const rootX = this.find(x);
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    const rootY = this.find(y);
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    if (rootX === rootY) return;
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    this.size--;
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    if (this.rank[rootX] > this.rank[rootY]) {
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      this.root[rootY] = this.root[rootX];
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    } else if (this.rank[rootX] < this.rank[rootY]) {
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      this.root[rootX] = this.root[rootY];
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    } else {
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      this.root[rootY] = this.root[rootX];
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      this.rank[rootX]++;
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    }
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  };
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}
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/**
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 * @param {number[][]} isConnected
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 * @return {number}
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 */
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var findCircleNum = function (isConnected) {
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  const n = isConnected.length;
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  const disjointSet = new DisjointSet(isConnected.length);
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  for (let i = 0; i < n; i++) {
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    for (let j = 0; j < n; j++) {
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      if (isConnected[i][j]) {
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        disjointSet.union(i, j);
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      }
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    }
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  }
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  return disjointSet.size;
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};