Generic min heap class for JS (which lacks that DS built-in)

min-heap.js

class MinHeap {
    constructor(selector = x => x[0]) {
        this.items = [0];
        this.selector = selector;
    }
    insert(item) {
        let childIdx = this.items.length;
        this.items.push(item);
        let childItem = item;
        let parentIdx = Math.trunc(childIdx/2), parentItem = this.items[parentIdx];

        while (childIdx > 1 && this.selector(parentItem) > this.selector(childItem)) {
            [this.items[childIdx], this.items[parentIdx]] = [parentItem, childItem];
            childIdx = parentIdx;
            childItem = this.items[childIdx];
            parentIdx = Math.trunc(childIdx/2);
            parentItem = this.items[parentIdx];
        }
    }
    remove() {
        let initialLen = this.items.length - 1;
        if (initialLen == 1)
            return this.items.pop();
        else if (initialLen <= 0)
            return undefined;
        const itemToReturn = this.items[1];
        this.items[1] = this.items.pop();
        let parentIdx = 1;
        let leftChildIdx;

        // Remember that heaps are complete trees--left is assigned before right
        while ((leftChildIdx = parentIdx*2) < initialLen) {
            let rightChildIdx = leftChildIdx + 1;
            let smallerChildIdx;
            if (rightChildIdx >= initialLen) {
                smallerChildIdx = leftChildIdx;
            } else {
                smallerChildIdx = this.selector(this.items[leftChildIdx]) < this.selector(this.items[rightChildIdx]) ?
                    leftChildIdx : rightChildIdx;
            }

            let parentItem = this.items[parentIdx];
            let smallerChildItem = this.items[smallerChildIdx];
            if (this.selector(parentItem) > this.selector(smallerChildItem)) {
                [this.items[smallerChildIdx], this.items[parentIdx]] = [parentItem, smallerChildItem];
                parentIdx = smallerChildIdx;
            } else {
                break;
            }
        }

        return itemToReturn;
    }
    isEmpty() {
        return this.items.length <= 1;
    }
    size() {
        return this.items.length-1;
    }
    peek() {
        if (this.items.length <= 1)
            return undefined;
        return this.items[1];
    }
}