js数组去重的四种方式

// 删除重复的
function only(arr){for(var i=0;i<arr.length;i++){for(var j = i+1;j<arr.length;j++){if(arr[i]===arr[j]){arr.splice(j,1);j--;}}}return arr;
}
console.log(only([6]));//[6]
console.log(only([1,9,8,8,0,6,0,6]));//[1, 9, 8, 0, 6]// 往新数组中插入不重复的元素或在最后一个位置的重复元素
function only(arr){
var newArr = [],
len = arr.length;
for(var i = 0;i<len;i++){for(var j = i+1;j<len;j++){if(arr[i]===arr[j]){j = false;break;}}if(j){newArr.push(arr[i]);}
}
return newArr;
}
console.log(only([6]));//[6]
console.log(only([1,9,8,8,0,6,0,6]));//[1, 9, 8, 0, 6]//往新数组中插入不重复的元素或在最后一个位置的重复元素
//难理解一些，关键是“j = ++i;”，相当于开启新一轮的i循环（外层循环）
function only(arr){var newArr = [],len = arr.length;for(var i = 0;i<len;i++){for(var j = i+1;j<len;j++){if(arr[i] === arr[j]){j = ++i;}}newArr.push(arr[i]);}return newArr;
}
console.log(only([6]));//[6]
console.log(only([1,9,8,8,0,6,0,6]));//[1, 9, 8, 0, 6]//将数组元素设为对象属性，值为true；如重复，不再添进数组
function only(arr){var newArr = [],obj = {},m;for(var i = 0;(m = arr[i]) !== undefined;i++){if(!obj[m]){newArr.push(arr[i]);obj[m] = true;}}return newArr;
}
console.log(only([6]));//[6]
console.log(only([1,9,8,8,0,6,0,6]));//[1, 9, 8, 0, 6]