HasOwnProperty () method User Guide in javascript, hasownproperty

HasOwnProperty () method User Guide in javascript, hasownproperty

Overview

The hasOwnProperty () method is used to determine whether an object contains the specified attributes.

Syntax
Obj. hasOwnProperty (prop)

Parameters

• Prop

• Name of the property to be detected.

Description

All inherited objects. all prototype objects are inherited from the prototype chain to the hasOwnProperty method. This method can be used to detect whether an object contains specific attributes, which is different from the in operator, this method ignores the attributes inherited from the prototype chain.

Example

Example 1: Use the hasOwnProperty method to determine whether an object contains specific attributes.

The following example checks whether the object o contains its own property prop:

Copy codeThe Code is as follows:
O = new Object (); o. prop = 'exists'; function changeO (){
O. newprop = o. prop;
Delete o. prop;} o. hasOwnProperty ('prop ');
// Return true
ChangeO ();
O. hasOwnProperty ('prop ');
// Return false

Example 2: differences between attributes

The following example demonstrates the difference between the hasOwnProperty method and the inherited attributes:

Copy codeThe Code is as follows:
O = new Object (); o. prop = 'exists'; o. hasOwnProperty ('prop ');
// Return true
O. hasOwnProperty ('tostring ');
// Return false
O. hasOwnProperty ('hasownproperties ');
// Return false

Example 3: traverse all attributes of an object

The following example demonstrates how to ignore the inheritance attribute when traversing all the attributes of an object .. the in loop only traverses the enumerated attributes, which is usually what we want and directly uses the Object. the getOwnPropertyNames () method can also meet similar requirements.

Copy codeThe Code is as follows:
Var buz = {
Fog: 'stack '};
For (var name in buz ){
If (buz. hasOwnProperty (name )){
Alert ("this is fog (" + name + ") for sure. Value:" + buz [name]);
}
Else {
Alert (name );
// ToString or something else
}}

Example 4: The hasOwnProperty method may be masked.

If an object has its own hasOwnProperty method, the method of the same name on the prototype chain will be masked (shadowed ):

Copy codeThe Code is as follows:
Var foo = {
HasOwnProperty: function (){
Return false;
},
Bar: 'Here be dragons'}; foo. hasOwnProperty ('bar ');
// Always return false
// If you are worried about this situation, you can directly use the real hasOwnProperty method on the prototype chain.
({}). HasOwnProperty. call (foo, 'bar ');
// True
Object. prototype. hasOwnProperty. call (foo, 'bar ');
// True

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