Detailed examples of new array methods in ES6

This article mainly introduces the new methods of array array in ES6. It summarizes and analyzes the functions and usage skills of various new methods of array array in ES6 in the form of examples. Friends in need can refer to it. I hope it can help everyone.

●find:

let arr=[1,2,234,'sdf',-2];
arr.find(function(x){
  return x<=2;
})//结果：1，返回第一个符合条件的x值
arr.find(function(x,i,arr){
  if(x<2){console.log(x,i,arr)}
})//结果：1 0 [1, 2, 234, "sdf", -2]，-2 4 [1, 2, 234, "sdf", -2]

The parameter of find is the callback function. The callback function can receive 3 parameters, value x, so i, array arr, the callback function returns the default value x.

●findIndex:

let arr=[1,2,234,'sdf',-2];
arr.findIndex(function(x){
  return x<=2;
})//结果：0，返回第一个符合条件的x值的索引
arr.findIndex(function(x,i,arr){
  if(x<2){console.log(x,i,arr)}
})//结果：1 0 [1, 2, 234, "sdf", -2]，-2 4 [1, 2, 234, "sdf", -2]

findIndex is similar to find, but returns the index by default.

●includes:

let arr=[1,2,234,'sdf',-2];
arr.includes(2);// 结果true，返回布尔值
arr.includes(20);// 结果：false，返回布尔值
arr.includes(2,3)//结果：false，返回布尔值

includes function is the same as string’s includes, receiving 2 parameters, the query item and the query starting position.

●keys:

let arr=[1,2,234,'sdf',-2];
for(let a of arr.keys()){
  console.log(a)
}//结果：0,1,2,3,4 遍历了数组arr的索引

keys, traversal of array index

●values:

let arr=[1,2,234,'sdf',-2];
for(let a of arr.values()){
  console.log(a)
}//结果：1,2,234,sdf,-2 遍历了数组arr的值

keys, traversal of array items

●entries:

let arr=['w','b'];
for(let a of arr.entries()){
  console.log(a)
}//结果：[0,w],[1,b]
for(let [i,v] of arr.entries()){
  console.log(i,v)
}//结果：0 w,1 b

entries, Traverse array key-value pairs.

●fill:

let arr=['w','b'];
arr.fill('i')//结果：['i','i']，改变原数组
arr.fill('o',1)//结果：['i','o']改变原数组,第二个参数表示填充起始位置
new Array(3).fill('k').fill('r',1,2)//结果：['k','r','k']，第三个数组表示填充的结束位置

The fill method changes the original array. When the third parameter is greater than the length of the array, it ends with the last digit. Location.

●Array.of():

Array.of('w','i','r')//["w", "i", "r"]返回数组
Array.of(['w','o'])//[['w','o']]返回嵌套数组
Array.of(undefined)//[undefined]依然返回数组
Array.of()//[]返回一个空数组

The Array.of() method always returns an array. The parameters are not classified into types, only Quantity, a quantity of 0 returns an empty array.

●copyWithin:

["w", "i", "r"].copyWithin(0)//此时数组不变
["w", "i", "r"].copyWithin(1)//["w", "w", "i"],数组从位置1开始被原数组覆盖，只有1之前的项0保持不变
["w", "i", "r","b"].copyWithin(1,2)//["w", "r", "b", "b"],索引2到最后的r,b两项分别替换到原数组1开始的各项，当数量不够，变终止
["w", "i", "r",'b'].copyWithin(1,2,3)//["w", "r", "r", "b"]，强第1项的i替换为第2项的r

The copyWithin method receives three parameters, the beginning of the replaced data, the beginning of the replacement block, and the replacement block The end of (not included);copyWithin(s,m,n).

●Array.from():

Array.from({'0':'w','1':'b',length:2})//["w", "b"],返回数组的长度取决于对象中的length，故此项必须有！
Array.from({'0':'w','1':'b',length:4})//["w", "b", undefined, undefined],数组后2项没有属性去赋值，故undefined
Array.from({'0':'w','1':'b',length:1})//["w"],length小于key的数目，按序添加数组

let ps=document.getElementsByTagName('p');
Array.from(ps)//返回p元素数组
Array.from('wbiokr')//["w", "b", "i", "o", "k", "r"]
Array.from([1,2,3],function(x){
    return x+1})//[2, 3, 4],第二个参数为回调函数

Array .from can convert array-like objects with length attributes into arrays, or it can convert traversable objects such as strings into arrays. It receives two parameters, the conversion object and the callback function.

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