jQuery source code analysis makeArray method

In jQuery, makeArray is a private method, which is mainly used to convert "array-like objects" Convert to array.

So what is "array-like object"?

For example, there is an arguments object in each function , which is a list of actual parameters and has the #length attribute. The actual parameters can also be accessed through subscripts.

	function foo(){
		//1
		console.log(arguments.length);
		//10
		console.log(arguments[0]);
	}
	
	foo(10);

In addition, objects of type HTMLCollection, NodeList are also "Array-like object".

They have 2 points in common:

1. They have the length attribute.

2. Elements can be accessed through subscripts.

Compared with arrays, array-like objects lack many convenient APIs, so many frameworks provide conversion methods.

The easiest way is to use the slice method on Array.prototype:

	function makeArray(array){
		return Array.prototype.slice.call(array);
	}	

But jQuery for compatibility The early IE provided its own implementation.

	
	var makeArray = function(array){
		//存储元素的新数组
		var ret = [];
		if(array != null){
			var i = array.length;
			/*
				分别对应四种非类数组对象情况：
				1.没有length属性
				2.为字符串
				3.是函数
				4.是window对象
			*/
			if(i == null || typeof array === "string" || jQuery.isFunction(array) || array.setInterval)
				ret[0] = array;
			else
				while(i)
					ret[--i] = array[i];
		}
		return ret;
	};

Its impact is 3:
1. Even if no parameters are passed, an empty array will be returned.

2. If array-like object is passed, a new element array will be returned.

3. If a non-array object is passed in, this object will be used as the first element of the new array.

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