How to convert array-like object to array in es6

Conversion method: 1. Use the "for in" statement to convert the array-like object into an array, the syntax is "for(var i in obj){console.log(arr.push(obj[i])); }"; 2. Use the built-in object keys and values, the syntax "Object.keys(obj)" and "Object.values(obj)"; 3. Use the from() function of the Array object, the syntax "Array.from(obj) ".

The operating environment of this tutorial: Windows 7 system, ECMAScript version 6, Dell G3 computer.

#What is an array class?

There are some objects in JavaScript that look like but are not arrays, called array-like objects.

#What is an array-like object?

only contains integers starting from 0 and naturally increasing integers as keys, and also defines length objects used to represent the number of elements. is usually considered to be a -like array object.

• has a numeric index subscript pointing to the object element, and the length attribute tells us the number of elements in the object;

• does not have For example, array objects such as push, forEach and indexOf have methods;

Convert class array to array

First method: Use for in to convert an array-like object into an array

<script type="text/javascript">
		var obj = {
			0: &#39;a&#39;,
			1: &#39;b&#39;,
			2: &#39;c&#39;,
		};
		console.log(obj[0]);
		console.log(typeof obj);
		var arr = [];
		for(var i in obj){
			console.log(arr.push(obj[i]));
		}
		console.log(arr);
		//把类数组对象放在一个名为arr的新数组里使得obj变成了数组

		console.log(arr instanceof Array);//判断arr是否为数组

	</script>

If you want to get the entire object:

let arr1 = []
		for (let i in obj) {
			let newobj = {}
			newobj[i] = obj[i]
			arr1.push(newobj);
		}
		console.log(arr1);

The second method: built-in object keys and values

Built-in object Object.keys: Get the key

Built-in object Object.values ​​gets the value

let obj = {
			'1': 5,
			'2': 8,
			'3': 4,
			'4': 6
		};
		//内置对象Object.keys：获取键
		var arr = Object.keys(obj)
		console.log(arr);
		//内置对象Object.values获取值
		var arr2 = Object.values(obj)
		console.log(arr2);

## The third method: Array.from( )

let obj = {
		'0': 5,
		'1': 8,
		'2': 4,
		'3': 6,
		'length':4
	};
	    let arr = Array.from(obj)
		console.log(arr);

Array.from() converts the object into an array and must meet 2 conditions

1: The key must be a numerical value

2: A key-value pair that must have length

##Expand knowledge: the difference between for of, for in and forEach

let arr = ['周一', '周二', '周三', '周四','周五','周六','周日']
		// for of
		for (let item of arr) {
			console.log(item);
		}
        // for in
		for (let i in arr) {
			console.log(i);
		}
        // forEach
        arr.forEach(item => {
			console.log(item);
		})