throttle 节流

在一定的时间范围内只执行一次

const throttle = function(fn, delay) {
    let previous = 0;
    let timer = null;
    return function run(... args) {
        const now = new Date();
        const remaining = delay - (now - previous);
        //间隔时间超过delay则立马执行
        //remaining > delay指的是客户端修改了时间，导致remianing > delay也会立马执行
        if (remaining < 0 || remaining > delay) {
            previous = now;
            fn.call(this, args);
        } else if (!timer) {
            timer = setTimeout(() => {
                previous = new Date();
                clearTimeout(timer);
                timer = null;
                fn.call(this, args);
            }, remaining);
        }
    };
};

debounce防抖

在一定时间内若重复操作，则重新计算开始时间

function debounce(fn, delay) {
    let previous = 0;
    let timer = null;
    return function proxy(...args) {
        if (!timer) {
            timer = setTimeout(() => {
                previous = new Date();
                clearTimeout(timer);
                timer = null;
                fn.call(this, args)
             },delay);
        }
    }
}