The meaning of function throttling and anti-shake

function debounce(fn, delay, immediate){
    var timeout,
        args,
        context,
        timestamp,
        result;    
        var later = function(){
        var last = Date.now() - timestamp;       
        if(last < delay && last >= 0){
            timeout = setTimeout(later, delay - last);
        }else{
            timeout = null;            
            if(!immediate){
                result = fn.apply(context, args);                
                if(!timeout){
                    context = args = null;
                }
            }
        }
    };    return function(){
        context = this;
        args = arguments;
        timestamp = Date.now();
        console.log(timestamp);        
        var callNow = immediate && !timeout;        
        if(!timeout){
            timeout = setTimeout(later, delay);
        }        if(callNow){
            result = fn.apply(context, args);
            context = args = null;
        }        return result
    }
};function throttle(method , duration ,delay ){
    var timer = null, 
        // 记录下开始执行函数的时间
        begin = new Date();    
        return function(){
        var context = this, 
            args = arguments, 
            // 记录下当前时间
            current = new Date();        // 函数节流里的思路
        clearTimeout(timer);        // 记录下的两个时间相减再与duration进行比较
        if(current-begin >= duration){
             method.apply(context , args);
             begin = current;
        }else{  
            timer = setTimeout(function(){
                method.apply(context , args);
            } , delay);
        }
    }
}
window.onresize = throttle(function(){console.log(&#39;resize&#39;)},1000,500)