How to determine the array? Some friends should know, but some can't tell how js judges arrays. The editor below has collected and sorted out some information for you on this issue. Friends who are interested can take a look at it. I hope you can master the knowledge of JS to judge arrays.
typeof operator
typeof will return a string of this type
var a = '123' console.log(typeof(a)) //string var b = [] console.log(typeof(b)) //object var c = {} console.log(typeof(c)) //object var d = null console.log(typeof(d)) //object
As seen above, the array object null is returned by typeof. This method cannot identify whether it is an object. Array
Prototype contructor chain method
Instantization has a contructor attribute. This attribute points to the method of generating an object array
var a = [] console.log(a.__proto__.constructor) //ƒ Array() { [native code] } var b = {} console.log(b.__proto__.constructor) //ƒ Object() { [native code] }
As seen above, the array is an object instantiated by the Array function. Instantiated by the Object function
I feel that this method is OK, but the constructor property can be overwritten
var a = [] a.__proto__.constructor = Object console.log(a.__proto__.constructor) //ƒ Object() { [native code] }
You can see that this has become an array and judged to be an object, so this The method is not the best either
instanceof
This method is to determine whether the object pointed to by the prototype attribute of a certain constructor is on the prototype chain of another object to be detected
var a = [] console.log(a instanceof Array) //a对象的原型链上能找到Array true console.log(a instanceof Object) //true 原型链上也能找到对象
The above is not particularly easy to determine whether it is an array or an object
General method toString
toString() method returns the string showing this object
var a= '123' console.log(a.toString()) //123 var b = [1,2,3] console.log(b.toSting()) //1,2,3 var c = {} console.log(c.toString)) //[object Object]
You can see that only the object returns the object type
Returns [object type] type represents the type of the object
To determine the object, use the toString method of Object to take it and use
var a =[] Object.prototype.toString.call(a) //[object Array]
this object The toString method can determine whether it is an array
But please note that there is a situation where toString() on the object prototype can also be changed
Array.isArray(XX)
My personal feeling is to use the general method toString() method Reliable
Related recommendations:
JS determines whether an array contains a string variable
How to use the in_array function to determine an array in JavaScript Detailed explanation of usage
Commonly used methods in PHP to determine whether an array is empty (five methods)
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