How to convert non-array objects into arrays

This time I will show you how to convert a non-array object into an array, and what are the precautions for converting a non-array object into an array. The following is a practical case, let's take a look.

Preface

Array.prototype.slice.call(obj)

let obj = {
 '0': 3,
 '1': 13,
 '2': 23,
 '3': 33,
 'length': 3,
 'name': 330
}
let arr = Array.prototype.slice.call(obj)
// [3, 13, 23]

[].slice.call(obj)

Array.from(obj)

• Array, Set, Map and String are all iterable objects (WeakMap/WeakSet are not iterable objects)

• String changes Became an iterable object, solving the coding problem

• These objects have default iterators, that is, they have the Symbol.iterator attribute

• You can use the for of loop

• All iterators created through generators are iterable objects

• document. getElementsByTagName<a href="http://www.php.cn/code/8145.html" target="_blank">("p") </a>Returns an iterable object but not an array
  Array.isArray(document.getElementsByTagName('p')) Returns false

let obj = {
 '0': 3,
 '1': 13,
 '2': 23,
 '3': 33
}
function *createIterator(obj){
 for(let value in obj){
  yield obj[value]
 }
}
let iterator = createIterator(obj)
let arr = Array.from(iterator)
// [3, 13, 23, 33]

Symbol.iterator property, you can turn it into an iterable object

let obj = {
 '0': 3,
 '1': 13,
 '2': 23,
 '3': 33
}
obj[Symbol.iterator] = function* () {
 for(let value in this){
  yield this[value]
 }
}
let arr = Array.from(obj)
// [3, 13, 23, 33]

typeof obj[Symbol.iterator] === 'function'

Traverse the enumerable properties of the object, including properties on its prototype chain, and the order is not guaranteed

hasOwnProperty() method to determine whether the property is the object's own property

Object.getOwnPropertyNames(obj) , return the object itself to be enumerable Enumerable or non-enumerable attributes

Object.assign() The method changes the values ​​​​of all enumerable attributes from one or more Source object copies to target object

[…obj]

[...'obj'] Returns ["o", "b", "j"]

[...new Set('objobj')]

##Object.values(obj)By default, the objects defined by the developer are all non-iterable objects, but methods are provided to return iterators

entries()
values()

• ##keys()

• By using these methods, you can return the related array

与类数组对象需要对象有 length 值不同，Object.values(obj) 返回对象自身可枚举属性值的集合

let obj = {
 '0': 3,
 '1': 13,
 '2': 23,
 '3': 33
}
let arr = Object.values(obj) // [3, 13, 23, 33]

字符串与数组的关系

在很大程度上，可以将字符串看成字符串数组，

都有 length 属性

都有 concat() / indexOf() / includes() / slice() 方法

不过值得注意的是， string 上没有方法可以原地修改它自身的内容，都是返回新的 string

string 还有个 repeat() 方法，创建指定数量的字符串副本

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