Array is used in js. For example, if multiple inputs with the same name are dynamically generated, You need to determine whether the input is an array. 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.
For more javascript Information, visit www.jb51.net.
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.
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