JS判断变量是不是数组

判断变量是不是数组有很多种，下面列出几种常见的：

1.数组方法 isArray()

        let a1 = [1,2,3]
        console.log(Array.isArray(a1))

2. 构造函数 constructor

        let a2 = [1,2,3]
        console.log(a2.constructor.toString().indexOf('Array'))

3. isPrototypeOf()

        let a3 = [1,2,3]
        console.log(Array.prototype.isPrototypeOf(a3))

4. instanceof

        let a4 = [1,2,3]
        console.log( a4 instanceof Array)

5. call()

        let a5 = [1,2,3]
        console.log( Object.prototype.toString.call(a5).indexOf('Array'))