Determine whether a variable type is an array or an object

Because whether it is an array or an object, the return value of the typeof operation is object, so there is a need to distinguish between the array type and the object type:

Side 1: Through the length attribute: In general, the object does not have a length attribute value, its value is undefiend, and the length value of the array is of type number

　　Disadvantage: Very impractical. When the property of the object has length and its value is number (such as a class array), this method is invalid, and it is not recommended to use it. Just take a look.

*Square 2: Judging and distinguishing by instanceof

var arr = [1, 2, 3];
var obj = {
name: 'lyl',
age: 18,
1: 'name'
}
console.log(arr instanceof Array); //true
console.log(obj instanceof Array); //false

*Part 3: through the constructor

　　　　 var arr = [1, 2, 3 ];
        var obj = {
            name: 'lyl',
            age: 18,
            1: 'name'
        }
        console.log(arr.constructor === Array); //true
        console.log(obj.constructor === Array); //false

*Square 4: Through the toString() method, the toString() method defined by the array prototype and the object prototype is different

　　Principle reference: http://www.cnblogs.com/ziyunfei/archive/2012/11/05/2754156.html

　　　　 var arr = [1, 2, 3 ];
        var obj = {
            name: 'lyl',
            age: 18,
            1: 'name'
        }
        console.log(Object.prototype.toString.call(arr) === '[object Array]'); //true
        console.log(Object.prototype.toString.call(boj) === '[object Array]'); //false

方五：随便找一个数组仅有的方法，来判断数组和对象谁有该方法即可（样例以sort来举例）

　　　　 var arr = [1, 2, 3];
        var obj = {
            name: 'lyl',
            age: 18,
            1: 'name'
        }
　　
        console.log(arr.sort === Array.prototype.sort); //true
        console.log(obj.sort === Array.prototype.sort); //false

　　总结：方法应用权重：

　　　　优先使用方四toString，因为该方法几乎无缺陷。

　　　　Next, you can use the second instanceof and the third constructor

　　　　The rest of the methods can be played, not practical

Determine whether a variable type is an array or an object

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