Method of JS Judging type

In the actual project development, may often encounter data type of judgment, I also often go to degree niang, not carefully summed up, recently idle down to do a summary bar.

The basic data types of JavaScript are: Undefined, Null, Boolean, number, String. There is also a reference data type object, and on the basis of object to inherit more types, such as array,date,function, of course, including our own created constructors;

That how more rigorous to judge the type of data, in the development of the more important, the degree Niang saw a lot of methods, it boils down to three kinds:

1. Constructor (constructor)

The constructor property returns a reference to the array function that created this object, (A.constructor = = array)//A constructor for the instance is an array? True or False

Console.log ([].constructor = = Array); Console.log ({}.constructor = = Object); Console.log ("string". Constructor = = String); Console.log ((123). constructor = = number); Console.log (true.constructor = = Boolean);

2. instanceof (example)

instance, hence the name of righteousness, examples, examples, so instanceof used to judge whether a variable is an instance of an object

var a=[];console.log (a instanceof Array)//return True

3. toString

This method is more complex, do not do too much explanation, the following:

var arr = [];object.prototype.tostring.call (arr) = = ' [Object Array] ';

The method is more rigorous, and the corresponding other types of data are judged as: [Object object],[object String],[object number],[object Boolean]

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Method of JS Judging type