Like Promise.all, but limiting how many functions to run in parallel. https://deploytonenyures.blogspot.com/2019/12/promiseall-with-limit.html

PromiseAllWithLimit.js

//I'm calling "task" to a function that when executed returns a Promise
class PromiseAllWithLimit{
    constructor(tasks, maxItems){
        this.allTasks = tasks;
        this.maxItems = maxItems;
        this.taskResults = [];
        this.nextTaskId = 0;
        this.resolveAll = null; //points to the resolve function to invoke when all tasks are complete
        this.completedCounter = 0;
    }

    //tasks: Array of functions that return a Promise
    //returns a Promise that gets resolved when all tasks are done
    run(){
         while(this.nextTaskId < this.maxItems){
            this._runNextTask();
        }
        return new Promise((res) => this.resolveAll = res);
    }

    _runNextTask(){
        //we need this var to get it trapped in the closure to run in the task.then()
        let curTaskId = this.nextTaskId
        let nextTask = this.allTasks[this.nextTaskId];
        this.nextTaskId++;
        nextTask().then((result) => {
            this.completedCounter++;
            this.taskResults[curTaskId] = result;
            if (this.nextTaskId < this.allTasks.length){
                this._runNextTask();
            }
            else{
                //no more tasks to launch
                //if all tasks are complete, complete the All Promise
                if(this.completedCounter === this.allTasks.length){
                    this.resolveAll(this.taskResults);
                }
            }
        });
    }
}


function getRandomInt(max) {
    return Math.floor(Math.random() * Math.floor(max));
  }

  //returns Promise<string>
function getPost(postId){
    console.log("getPost " + postId + " started");
    return new Promise(res => {
        setTimeout(() => {
            console.log("---> getPost " + postId + " finishing");
            res(`${postId} - content`)
        }, 2000 * (1 + getRandomInt(2)));
    });
}

(async () => {
    let tasks = [];
    for (let i=0; i<10; i++){
        tasks.push(() => getPost("postId_" + i));
    }
    let results = await new PromiseAllWithLimit(tasks, 5).run();
    console.log("all tasks are complete");
    console.log(results.join("\n"));
})();