I'm a bit puzzled about the concept of a read-only property. While MDN defines classList as such, can you clarify what this really entails?
I'm a bit puzzled about the concept of a read-only property. While MDN defines classList as such, can you clarify what this really entails?
When a property is declared as read-only, it means that it cannot be changed or reassigned. Any attempt to do so will have no effect in non-strict mode. For example:
var obj = {};
Object.defineProperty(obj, 'property', {value: 123, writeable: false})
// Trying to update obj.property with the value 456 using the . syntax will not change its value
obj.property = 456;
console.log(obj.property);
// Attempting to set obj.property to 789 using the [] syntax will also keep the value as 123
obj['property'] = 789;
console.log(obj['property']);In strict mode, any such attempts will result in a TypeError:
'use strict';
var obj = {};
Object.defineProperty(obj, 'property', {value: 123, writeable: false})
// Trying to assign 456 to obj.property in strict mode will throw a TypeError
obj.property = 456;
console.log(obj.property);When a property is marked as read-only, it is considered to be "non-writable" and cannot be changed or reassigned.
For instance, you are unable to update or modify the value of the classList property for an element, but you can still access its current value.
If you want more information on this topic, check out these resources:
In addition to the information shared by @Mureinik, there is an alternative method to create a read-only object using the freeze function. Here is an example of how you can implement it:
let myObj = {id: 45, title: 'title here'}
Object.freeze(myObj);
myObj.title = 'update title' // this change will not be applied
console.log(myObj)
// To modify a frozen object, you must reassign all its properties
// For instance:
myObj = {id: myObj.id, title: 'Another title here'}
console.log(myObj)If you want to learn more about Object.freeze() and the proper way to update it, visit the mdn documentation.
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