Kruskal

function kruskals(gNodes, gFrom, gTo, gWeight) {
    // Need union find (disjoint set data-structure for the solution)
    function UnionFind(count) {
        this.roots = Array(count);
        this.ranks = Array(count);
        for (let i = 0; i < count; ++i) {
            this.roots[i] = i;
            this.ranks[i] = 0;
        }
    }
    UnionFind.prototype.find = function (x) {
        let root = x;
        // Find the root of the component
        const roots = this.roots;
        while (roots[root] !== root) {
            root = roots[root];
        }
        // Compress the path leading back to the root
        // "Path compression"
        // Gives amortized constant time complexity
        while (root !== x) {
            const next = roots[x];
            roots[x] = root;
            x = next;
        }
        return root;
    };
    UnionFind.prototype.union = function (x, y) {
        const xr = this.find(x);
        const yr = this.find(y);
        if (xr === yr) {
            return;
        }
        const ranks = this.ranks;
        const roots = this.roots;
        const xd = ranks[xr];
        const yd = ranks[yr];
        if (xd < yd) {
            roots[xr] = yr;
        } else if (xd > yd) {
            roots[yr] = xr;
        } else {
            roots[yr] = xr;
            ++ranks[xr];
        }
    };
    // have a list of edges with weights
    const tree = [];
    gFrom.forEach((el, i) => {
        const edge = {};
        edge.v1 = el;
        edge.v2 = gTo[i];
        edge.weight = gWeight[i];
        tree.push(edge);
    });
    // sort the edges in ascending order
    tree.sort((a, b) => a.weight - b.weight);
    const djSet = new UnionFind(gNodes);
    let totalWeight = 0;
    tree.forEach((edge) => {
        // for each edge, find a root
        const r1 = djSet.find(edge.v1);
        const r2 = djSet.find(edge.v2);
        // if edges don't belong to the same set
        // unite them and increase total weight
        // to find minimum spanning tree
        if (r1 !== r2) {
            totalWeight += edge.weight;
            djSet.union(r1, r2);
        }
    });
    return totalWeight;
}