Fancy Sequence LeetCode solution in JavaScript

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var Fancy = function () {
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  this.sequence = [];
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  this.appliedOps = [];
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  this.ops = [];
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  this.modulo = Math.pow(10, 9) + 7;
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};
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/**
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 * @param {number} val
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 * @return {void}
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 */
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Fancy.prototype.append = function (val) {
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  this.sequence.push(val);
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  this.appliedOps.push(this.ops.length);
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};
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/**
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 * @param {number} inc
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 * @return {void}
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 */
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Fancy.prototype.addAll = function (inc) {
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  this.ops.push(["add", inc]);
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};
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/**
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 * @param {number} m
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 * @return {void}
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 */
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Fancy.prototype.multAll = function (m) {
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  this.ops.push(["mult", m]);
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};
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/**
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 * @param {number} idx
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 * @return {number}
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 */
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Fancy.prototype.getIndex = function (idx) {
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  if (idx >= this.sequence.length) {
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    return -1;
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  }
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  while (this.appliedOps[idx] < this.ops.length) {
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    const [operation, value] = this.ops[this.appliedOps[idx]];
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    this.appliedOps[idx]++;
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    if (operation === "mult") {
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      this.sequence[idx] = (this.sequence[idx] * value) % this.modulo;
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    }
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    if (operation === "add") {
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      this.sequence[idx] = (this.sequence[idx] + value) % this.modulo;
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    }
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  }
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  return this.sequence[idx];
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};
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/**
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 * Your Fancy object will be instantiated and called as such:
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 * var obj = new Fancy()
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 * obj.append(val)
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 * obj.addAll(inc)
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 * obj.multAll(m)
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 * var param_4 = obj.getIndex(idx)
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 */