方法1：两层for循环，外层循环原数组，内层循环时进行比较。

Array.prototype.removal = function(){
 var arr = this,
  result = [],
  i,
  j,
  len = arr.length;
 for(i = 0; i < len; i++){
  for(j = i + 1; j < len; j++){
    if(arr[i] === arr[j]){
    j = ++i;
    }
  }
  result.push(arr[i]);
 }
 return result;
}
var arr1 = [1,2,3,4,2,3,1,4,5,6,6];
arr1.removal();//返回[2,3,1,4,5,6]

方法2：利用对象的属性不能相同的特点去重

Array.prototype.removal = function(){
 var arr = this,
 i,
 obj = {},
 result = [],
 len = arr.length;
 for(i = 0; i < len; i++){
   if(!obj[arr[i]]){
     obj[arr[i]] = 1;
     result.push(arr[i]);
   }
 }
 return result;
}
var arr1 = [1,2,3,4,2,3,1,4,5,6,6];
arr1.removal();//返回[1,2,3,4,5,6]

方法3：利用splice直接在原数组进行操作

Array.prototype.removal = function(){
 var arr = this,
 i,
 j,
 len = arr.length;
 for(i = 0; i < len; i++){
    for(j = i + 1; j < len; j++){
       if(arr[i] == arr[j]){
         arr.splice(j,1);
         len--;
         j--;
       }
    }
 }
 return arr;
}
var arr1 = [1,2,3,4,2,3,1,4,5,6,6];
arr1.removal();//返回[1,2,3,4,5,6]

方法4：数组递归去重

Array.prototype.removal = function(){
 var arr = this,
 len = arr.length;
 arr.sort(function(a,b){
    return a - b;
 })
 function loop(index){
   if(index >= 1){
     if(arr[index] === arr[index-1]){
       arr.splice(index,1);
     }
     loop(index - 1); 
   }
 }
 loop(len-1);
 return arr;
}
var arr1 = [1,2,3,4,2,3,1,4,5,6,6];
arr1.removal();//返回[1,2,3,4,5,6]

方法5：利用indexOf以及forEach

Array.prototype.removal = function (){
 var arr = this,
  result = [],
  len = arr.length;
 arr.forEach(function(v, i ,arr){  
  var bool = arr.indexOf(v,i+1);  
  if(bool === -1){
   result.push(v);
  }
 })
 return result;
};
var arr1 = [1,2,3,4,2,3,1,4,5,6,6];
arr1.removal();//返回[1,2,3,4,5,6]

方法6.利用ES6的set

function removal(arr){
 return Array.from(new Set(arr));
}
removal([1,2,3,4,2,3,1,4,5,6,6]);//返回[1,2,3,4,5,6]