Usage of javascript typeof and introduction to the typeof operator [Details] Page 1/2

Arrays are often used in js. For example, if multiple inputs with the same name are generated dynamically, You need to determine whether the input is an array during submission.
If (document. mylist. length! = "Undefined") {} This usage is incorrect.
Correct is if (typeof (document. mylist. length )! = "Undefined "){}
Or if (! IsNaN (document. mylist. length )){}
The number of typeof operations is undefined, and "undefined" is returned ".
Number of operations: number typeof (x) = "number"
String typeof (x) = "string"
Boolean value typeof (x) = "boolean"
Object, array, and null typeof (x) = "object"
Function typeof (x) = "function"
The typeof operator returns a string that represents the Data Type of the expression.
Possible strings include: "number", "string", "boolean", "object", "function", and "undefined ".
For example:
Alert (typeof (123); // typeof (123) returns "number"
Alert (typeof ("123"); // typeof ("123") returns "string"
Typeof Operator
Returns a string that represents the expression's data type.
Typeof [() expression [];
The expression parameter is an arbitrary expression that needs to be searched for type information.
Description
The typeof operator returns the type information as a string. There are six possible types of typeof return values: "number," "string," "boolean," "object," "function," and "undefined ."
Parentheses in the typeof syntax are optional.