Linked List Random Node LeetCode solution in JavaScript

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var Solution = function (head) {
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  this.res = [];
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  let curr = head;
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  while (curr !== null) {
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    this.res.push(curr);
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    curr = curr.next;
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  }
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  this.length = this.res.length;
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};
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Solution.prototype.getRandom = function () {
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  //Math.random() will generate a random number b/w 0 & 1.
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  //then multiply it with the array size, as i have all the value in the list, i know the size of the list
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  //take only the integer part which is a random index.
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  //return the element at that random index.
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  return this.res[Math.floor(Math.random() * this.length)].val;
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};