JavaScript in operator __java

Definition:

The in operator is used to determine that an attribute belongs to an object, either as a direct property of an object or as an inherited property through prototype. (See hasOwnProperty) Precautions :

n for a Generic object property, you need to specify the name of the property with a string

Such as:

var Mycar = {make: "Honda", Model: "Accord", year:1998};

' Make ' in Mycar//returns True

"Model" in Mycar//returns True

n an indexed value that specifies a numeric form for an array property to represent the property name of the array (except for intrinsic attributes, such as length).

Arrays

var trees = new Array ("Redwood", "Bay", "Cedar", "oak", "maple");

0 in Trees//returns True

3 in Trees//returns True

6 in Trees//returns False

"Bay" in Trees//returns False (you must specify the index number,

Not the value in that index)

' Length ' in Trees//returns True (the length is a Array property)

The right side of N in must be an object, such as: You can specify a form that is generated with the string constructor, but you cannot specify a direct amount of string:

var color1 = new String ("green");

' Length ' in Color1//returns True

var color2 = "Coral";

"Length" in Color2//generates an error (color isn't a String object)

n If you Delete an attribute using the delete operator, it returns falseif you use the in check again,such as:

var Mycar = {make: "Honda", Model: "Accord", year:1998};

Delete Mycar.make;

' Make ' in Mycar; Returns false

var trees = new Array ("Redwood", "Bay", "Cedar", "oak", "maple");

Delete Trees[3];

3 in trees; Returns false

n If you set a property value to undefinedbut do not use the delete operator, using in check will return true.

var Mycar = {make: "Honda", Model: "Accord", year:1998};

Mycar.make = undefined;

' Make ' in Mycar; Returns True

var trees = new Array ("Redwood", "Bay", "Cedar", "oak", "maple");

TREES[3] = undefined;

3 in trees; Returns True