js 高级函数

function animation(duration,from,to,handler){
    const dis=to-from;
    const speed=dis/duration;
    const startTime=Date.now();
    let value=from;
    handler(value);
    function _run(){
        const now=Date.now();
        const time=now-startTime;
        if(time>=duration){
            value=to;
            return 
        }
        const d=time*speed;
        value=from+d;
        handler(value);
        requestAnimationFrame(_run);
    }
    requestAnimationFrame(_run);
}

function debounce(fun,delay){
    let timerId=null;
    return function(...args){
        timerId && clearTimeout(timerId);
        timerId=setTimeout(()=>{
            fun.apply(this,args)
        },delay)
        
    }
}

function paralleltask(tasks,parallelCount){
    return new Promise(resolve=>{
        if(tasks.length===0){
            resolve();
            return;
        }
        let nextIndex=0;
        let taskFinish=0;
        function _run(){
            const task=tasks[nextIndex];
            nextIndex++;
            task().then(()=>{
                taskFinish++;
                if(nextIndex<tasks.length){
                    _run();
                }else{
                    if(taskFinish===tasks.length){
                        resolve();
                    }
                }
            })
        }
        for(let i=0;i<parallelCount && i<tasks.length;i++){
            _run();
        }
    })
   
}

function groupby(arr,generatekey){
    const newObj={};
    for(let item of arr){
        const key=generatekey(item);
        if(!newObj[key]){
            newObj[key]=[]
        }
        newObj[key].push(item)
    }
    return newObj
}


function parallelRendertask(taskdatas,renderTask){
    if(taskdatas.length===0){
        return;
    }
    let i=0;
    function _run(){
        if(i===taskdatas.length){
            return;
        }
        requestIdleCallback(idle=>{
            while(idle.timeRemaining()>0 && i<taskdatas.length){
                //做相应的渲染任务
                renderTask(taskdatas[i]);
                i++;
            }
            _run;
        })       
    }
    _run();
}