Attributes of an object's properties in JavaScript

Enumberable: Indicates whether the property can be returned through the for-in loop. Default is True

Writable: Whether the property can be modified by default to True

Value: The data value that contains this property. When reading a property value 3, read from this property, write the property, save the new value to this location. The default value is Undefine.

Getter: The function that is called when the property is read

Setter: The function that is called when the property is written

Special note: Once the Object.defineproperty method is called, those undefined attribute values except configurable are false, the others are undefined;

2. Modify the properties of a single attribute:

You must use the Object.defineproperty () method. This method takes 3 parameters: the object where the property resides, the name of the property, and a descriptor object. The properties of the Descriptor object must be: Configurable, enumberable, Writable,value. Set one or more of these values to modify the corresponding attribute values.

Modify the writable attribute, set to false so that the property value cannot be modified as follows:

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var person = {};object.defineproperty (person, "name", {writable:false,//) the attribute of the Set property is non-modifiable value: "Tom"//Set the Name property value to Tom}); Person.name = "Jany"; An attempt was made to set the Name property value to Jany, but failed. This statement is ignored in non-strict mode, and strict mode will error Console.log (person.name); The result is still Tom

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Lines 2nd to 6th we set the value of the Name property to Tom, and set its writable property to False, and then we tried to change it to jany in 7 rows, but the final print was still zzy.

Modify the Configurabel attribute, set to false so that the property cannot be deleted (delete), as follows:

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var person = {};object.defineproperty (person, "name", {configurable:false,//set configurable to False value: "Tom"}); cons Ole.log (Person.name); Printing results for Tomdelete person.name; An attempt was made to remove the name attribute Console.log (person.name); But name still exists, print out Tom

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If we change the configurable property value to True, the property can be deleted

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var person = {};object.defineproperty (person, "name", {configurable:true, Value: "Tom"}); Console.log (person.name);//Hit Print out Tomdelete person.name; An attempt was made to remove the name attribute Console.log (person.name); Delete succeeded, print out udefined

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In addition, once we have set the properties of a property to be non-configurable, we can no longer change it back to configurable. At this point, calling the Object.defineproperty () method modifies an attribute other than writable to error.

As follows:

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person = {};object.defineproperty (person, "name", {configurable:, Value: "Tome"}); Object.defineproperty (person, "name ", {configurable:, Value:" Lyl "}); Console.log (Person.name);

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We will see the following error message in the browser:

Modifying getter and Setter properties

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Book = {_year:2004, Edition:1-};object.defineproperty (book, ' year ', {get: () {. _year;　　　　　　}, set: (NewValue) {(NewValue > 2004) {. _year = newvalue;　　　　. edition + = newValue-2004; }　　} }); Book.year = 2005;console.log (book.edition);

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3. Define (Modify) Properties of multiple attributes at the same time

Because there is a large likelihood of defining multiple properties, ES5 has a object.defineproperties method defined . This method allows you to define multiple properties at once by using a descriptor. This method accepts parameters for two objects, the first object is the object to add and modifier properties, and the second object's properties correspond to the order one by one to be added or modified in the first object.

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Book = {};object.defineproperties (book, {_year: {value:2004}, Edition: {value:1, writable:}, Y　　　　Ear: {get: () {. _year;　　　　　　　　}, set: (NewValue) {(NewValue > 2004) {. _year = newvalue;　　　　　　. edition + = newValue-2004; }　　　　}　　}}); Book.year = 2006;console.log (book.edition);

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4. Properties of the Read attribute

Attributes of an object's properties in JavaScript