Understanding the role of hasOwnProperty() in JAVASCRIPT_javascript skills

The hasOwnProperty function method in JavaScript returns a Boolean value indicating whether an object has a property with the specified name.

How to use hasOwnProperty():

object.hasOwnProperty(proName)
The parameter object is required. An instance of an object.
proName is required. A string value for the property name.

If the object has a property with the specified name, the hasOwnProperty function method in JavaScript returns true; otherwise, it returns false. This method cannot check whether the property is in the object's prototype chain; the property must be a member of the object itself. In the following example, all String objects share a common split method. The code below will output false and true.

Copy code The code is as follows:

var s = new String("JScript");
print(s.hasOwnProperty("split"));
print(String.prototype.hasOwnProperty("split"));

hasOwnProperty: is used to determine whether an object has a property or object with the name you gave it. However, it should be noted that this method cannot check whether the object has the property in the prototype chain. The property must be a member of the object itself. The format is as follows:

Js code

1. object.hasOwnProperty(proName);

Determine whether the name of proName is an attribute or object of the object object.

1. Example 1:

var bStr = "Test String".hasOwnProperty("split"); // Get false because the properties in the prototype chain cannot be detected

But:

"Test String".split(" "); can be called successfully

2. Example 2:

var bStr1 = String.prototype.hasOwnProperty("split"); //The prototype of the String object already has this property, so it naturally returns true

3. Example 3

var bObj = ({fnTest:function(){}}).hasOwnProperty("fnTest"); // Returns true because the property in the object exists

Object Object

Object The object itself is not very useful, but you should still understand it before understanding other classes. Because the Object object in ECMAScript is similar to the java.lang.object in Java, all objects in ECMAScript are inherited from this object. All properties and methods in the Object object will appear in other objects, so understand the Object object , you can better understand other objects.

Object objects have the following properties:

constructor
A reference (pointer) to the function that creates the object. For Object objects, this pointer points to the original Object() function.
Prototype
A reference to the object prototype of the object. For all objects, it returns an instance of the Object object by default.

Object objects also have several methods:

hasOwnProperty(property)
Determine whether the object has a specific property. This property must be specified as a string. (For example, o.hasOwnProperty("name"))
IsPrototypeOf(object)
Determine whether the object is the prototype of another object.
PropertyIsEnumerable
Determine whether the given property can be enumerated using the for...in statement.
ToString()
Returns the raw string representation of the object. For Object objects, ECMA-262 does not define this value, so different ECMAScript implementations have different values.
ValueOf()
Returns the original value that best fits this object. For many objects, the value returned by this method is the same as the return value of ToString()