JS中截取数组的几种方法总结

array.splice(start[,deleteCount[,item1[,item2[,...]]]])
//start :指定修改的开始位置（从0开始计数），如果超出了数组的长度，则从数组末尾开始添加内容；如果是负值，则表示从数组末位（从后往前数）开始的第n 位；如果负数的绝对值大于数组的长度，则表示开始的位置为第0位。
//deleteCount(可选) :整数，表示要删除的数组元素的个数。如果deleteCount大于start之后的元素的总数，则从start后面的元素都将被删除（包含第start位）；如果 deleteCount 是 0 或者负数，则不移除元素。这种情况下，至少应添加一个新元素。
// item1,item2(可选) :要添加进数组的元素，从start 位置开始。如果不指定，则 splice() 将只删除数组元素。
// 返回值 由被删除的元素组成的一个数组。如果只删除了一个元素，则返回只包含一个元素的数组。如果没有删除元素，则返回空数组。

const arr = ["a","b","c","d","e"]
var arr1 = arr.splice(3,1,"f") 
// 3 表示从索引为3的位置开始删除，
// 1 删除元素的个数
// 最后面是表示向原数组中添加元素，位置就是前面两个数字所定义的位置添加数据
console.log(arr) //原数组：arr["a", "b", "c", "f", "e"]
console.log(arr1)  // 返回值 --被删除的元素 arr1 ["d"]

const arr = ["a","b","c","d","e"]
var arr1 = arr.splice(2,2)  
console.log(arr)  //原数组：arr ["a", "b", "e"]
console.log(arr1) // 返回值 --被删除的元素 arr1 ["c", "d"]

const arr = ["a","b","c","d","e"]
var arr1 = arr.splice(1)  //从索引 1 的位置开始删除所有元素
console.log(arr)  //原数组：arr["a"]   
console.log(arr1) //返回值 --被删除的元素 arr1 ["b", "c", "d", "e"]

var animals = [
  { name: "Fluffykins", species: "rabbit" },
  { name: "Caro", species:"dog"},
  { name: "Hamilton", species: "dog" },
  { name: "Harold", species: "fish"},
  { name: "Ursula", species: "cat" },
  { name: "Jimmy", species: "fish" }
];
var dogs = animals.filter(x => x.species === "dog");
var dogs = animals.filter(item=>{
    return item.species === "dog"
})
console.log(dogs); 
// {name: "Caro", species: "dog"}
// { name: "Hamilton", species: "dog" }

var animals = [
  { name: "Fluffykins", species: "rabbit" },
  { name: "Caro", species:"dog"},
  { name: "Hamilton", species: "dog" },
  { name: "Harold", species: "fish"},
  { name: "Ursula", species: "cat" },
  { name: "Jimmy", species: "fish" }
];

var names = animals.map(x=>x.name);
var names = animals.map(item=>{
    return item.name
})
console.log(names); 
//["Fluffykins", "Caro", "Hamilton", "Harold", "Ursula", "Jimmy"]