javaScript语言精粹的二三代码+

早就耳闻《javaScript语言精粹》写的很经典，一定要反复读，自觉前端已初窥门径，而且这段时间又接触算法和ES6，看完之后的确很棒，原来理解不深的地方恍然大悟，对这门语言的优雅和糟粕也更加了然于心；这里把里面一些代码略作摘抄，也算是再加咀嚼代码是敲出来的

fade-background

var fade =(node)=>{
var level=1;
var step=()=>{
    var hex =level.toString(16);
    node.style.backgroundColor="#FFFF"+hex+hex;
    if(level<15){
       level+=1;
       setTimeout(step,100);
    }
 };setTimeout(step,100);
}
fade(document.body);

替html字符实体

Function.prototype.method=function(name,func){
       this.prototype[name]=func;
       return this;
};
String.method('deentityify',function(){
       var entity={
           quto:"''",
           lt:"<",
           gt:">"  
  };
  return function(){
        return this.replace(/&([^&;]+);/g,
               (a,b)=>{
                    var r=entity[b];
                    return typeof r==='string'?r:a;        
              }
             );        
  };
}());
console.log('&lt;&quto;&gt;&ll'.deentityify());
document.writeln('&lt;&quto;&gt;&ll'.deentityify());

去掉js数组中重复项

var arr=[1,2,3,3,2,3,5];
[...new Set(arr)];

function unique(arr) {
      var result = [], isRepeated;
      for (var i = 0, len = arr.length; i < len; i++) {
          isRepeated = false;
          for (var j = 0, len2 = result.length; j < len2; j++) {
              if (arr[i] == result[j]) {   
                  isRepeated = true;
                 break;
              }
         }
         if (!isRepeated) {
             result.push(arr[i]);
            
         }
     }
     return result;
 }
unique([1,1,2,3]);//从嵌套循环就可以看出，这种方法效率极低
function unique2(arr) {
    var result = [], hash = {};
    for (var i = 0, elem;  i<arr.length; i++) {
        (elem = arr[i]) != null;
        if (!hash[elem]) {
            result.push(elem);
            hash[elem] = true;
        }
    }
    return result;
}
unique2([1,2,1,23,3]);//用一个hashtable的结构记录已有的元素，这样就可以避免内层循环

js去除数组中的空元素

var array = [1,2,,,4,6,,,,,,55];
 
alert(array)
for(var i = 0 ;i<array.length;i++)
{
            if(array[i] == "" || typeof(array[i]) == "undefined")
            {
                     array.splice(i,1);
                     i= i-1;
                 
            }
             
}
 
alert(array);

memoization-fibonacci

var fibonacci=function(){
    var memo=[0,1];
    var fib=(n)=>{
        var result=memo[n];
        if(typeof result!=='number'){
            result=fib(n-1)+fib(n-2);
            memo[n]=result;
        }
             return result;
   };
	for(var i=0;i<=10;i++){
	   console.log('//'+i+':'+fib(i));
	   
	}
	console.log(memo);
}();

sort进阶

var a=[
	  {first:'Joe',last:'Besser'},
	  {first:'Moe',last:'Howard'},
	  {first:'Joe',last:'DeRita'},
	  {first:'Shemp',last:'Howard'},
	  {first:'Larry',last:'Fina'},
	  {first:'Curry',last:'Howard'}
	];
var by = function(name,minor){
	return function(o,p){
		var a,b;
		if(o && p && typeof o==='object'&&typeof p==='object'){
			a=o[name];
			b=p[name];
			if(a===b){
				return typeof minor==='function'?minor(o,p):0;
			}
			if(typeof a===typeof b){
				return a<b?-1:1;
			}
			return typeof a<typeof b?-1:1;
		}else{
			throw{
				name:'Error',
				message:'Expected an object when sorting by'+name
			};
		}
	};
};
a.sort(by('last'),by('first'));//[ { first: 'Joe', last: 'Besser' },
							   //{ first: 'Joe', last: 'DeRita' },
							   //{ first: 'Larry', last: 'Fina' },
							   //{ first: 'Moe', last: 'Howard' },
							   //{ first: 'Shemp', last: 'Howard' },
							   //{ first: 'Curry', last: 'Howard' } ]

未完待续。。。。。