over 7 years ago
To understand what configurable does, I did a little experiement:
var obj = {};
obj.name = 'cheng';
console.log(obj.name); // cheng
Object.defineProperty(obj, 'name', {configurable: false});
var des = Object.getOwnPropertyDescriptor(obj, 'name');
console.log('Writable: ' + des.writable); // true
console.log('Configurable: ' + des.configurable); // false
console.log('Enumerable: ' + des.enumerable); // true
delete obj.name; // the delete operation returns false
console.log(obj.name); // prints cheng
Object.defineProperty(obj, 'name', {writable: false});
des = Object.getOwnPropertyDescriptor(obj, 'name');
console.log('Writable: ' + des.writable); // false, so it is ok to change writable to false
Object.defineProperty(obj, 'name', {enumerable: false}); // "TypeError: Cannot redefine property: name, which means enumerable cannot be changed if configurable is set to false
I wonder if I can change those properties to true if they started as false:
var obj = {};
Object.defineProperty(obj, 'name', {configurable: false, writable:false, enumerable: false, value:'cheng'});
var des = Object.getOwnPropertyDescriptor(obj, 'name');
console.log('Writable: ' + des.writable); // false
console.log('Configurable: ' + des.configurable); // false
console.log('Enumerable: ' + des.enumerable); // false
Object.defineProperty(obj, 'name', {configurable: true}); // "TypeError: Cannot redefine property: name
Object.defineProperty(obj, 'name', {writable: true}); // "TypeError: Cannot redefine property: name
Object.defineProperty(obj, 'name', {enumerable: true}); // "TypeError: Cannot redefine property: name
Conclusion
When configurable is set fo false:
- you cannot
deletethe property by using the keyworddelete - you cannot change the property
enumerable - you CAN change the property
writablefromtrue to falsebut not the other way around - you cannot change
configurabletotrueif its current state isfalse
