Throttle

throttle.js

/*
 * @param {Function} func
 *   需要进行节流的函数
 * @param {number} wait
 *   节流的时间间隔
 * @param {boolean} [trail]
 *   是否要在结尾执行
 * @returns {Function}
 *   返回一个节流函数
 */
function throttle(func, wait, trail) {
    if ("function" !== typeof func) {
        throw new TypeError;
    }
    wait = +wait || 0;
    trail = !!trail;

    var tid, timestamp,
        that, args;

    function delayed(timeout) {
        tid = setTimeout(function () {
            handler();
            timestamp = now();
        }, timeout);
    }

    function now() {
        return Date.now ? Date.now() : new Date().getTime();
    }

    function handler() {
        return func.apply(that, args);
    }

    return function _() {
        args = arguments;
        that = this;

        var remaining = 0;

        trail && tid && clearTimeout(tid);

        if (!timestamp || (remaining = now() - timestamp) >= wait) {
            timestamp = now();
            handler();
        } else if (trail) {
            delayed(wait - remaining);
        }
    };
}