Flatten Nested List Iterator.js

// Runtime: 86 ms (Top 46.9%) | Memory: 54.48 MB (Top 31.0%)

/**
 * // This is the interface that allows for creating nested lists.
 * // You should not implement it, or speculate about its implementation
 * function NestedInteger() {
 *
 *     Return true if this NestedInteger holds a single integer, rather than a nested list.
 *     @return {boolean}
 *     this.isInteger = function() {
 *         ...
 *     };
 *
 *     Return the single integer that this NestedInteger holds, if it holds a single integer
 *     Return null if this NestedInteger holds a nested list
 *     @return {integer}
 *     this.getInteger = function() {
 *         ...
 *     };
 *
 *     Return the nested list that this NestedInteger holds, if it holds a nested list
 *     Return null if this NestedInteger holds a single integer
 *     @return {NestedInteger[]}
 *     this.getList = function() {
 *         ...
 *     };
 * };
 */
/**
 * @constructor
 * @param {NestedInteger[]} nestedList
 */
var NestedIterator = function(nestedList) {
    this.nestedList = []
    this.ptr = 0
    const dfs = (elem) => {
        if(!elem.isInteger()) {
            let list = elem.getList()
            for(let i = 0;i<list.length;i++) {
                dfs(list[i])
            }
        }else {
            this.nestedList.push(elem.getInteger())
        }
    }
    for(let i = 0;i<nestedList.length;i++) {
        dfs(nestedList[i])
    }
};


/**
 * @this NestedIterator
 * @returns {boolean}
 */
NestedIterator.prototype.hasNext = function() {
    if(this.ptr < this.nestedList.length) return true
    else return false
};

/**
 * @this NestedIterator
 * @returns {integer}
 */
NestedIterator.prototype.next = function() {
    return this.nestedList[this.ptr++]
};

/**
 * Your NestedIterator will be called like this:
 * var i = new NestedIterator(nestedList), a = [];
 * while (i.hasNext()) a.push(i.next());
*/