I'm trying to make the properties inside a constructor function immutable, i.e. the properties should not be altered either with a dot or bracket notation. E.g. I have my constructor function:
function OnceNamedOne() {
Object.freeze(this.firstName = 'John');
Object.freeze(this.lastName = 'Doe');
this.fullName = this.firstName + ' ' + this.lastName;
}
I basically want to freeze the properties and hard wire their values as in the function. So, when an instance is created:
var me = new OnceNamedOne(); and when the value I try to change the property value, it should not work - that is the following should not assign 'John' to first name: me.firstName = 'John';.
How could I do this?
You can't freeze a property with a primitive, but you could make it non-writable
Object.defineProperty(this, 'firstname', {
enumerable : false,
configurable : false,
writable : false,
value : 'John'
});
For multiple properties, it's probably easier to make a convenience function
function createNonWritable(obj, key, value) {
Object.defineProperty(obj, key, {
enumerable : false,
configurable : false,
writable : false,
value : value
});
}
function OnceNamedOne() {
createNonWritable(this, 'firstname', 'John');
createNonWritable(this, 'lastname', 'Doe');
createNonWritable(this, 'fullname', this.firstname + ' ' + this.lastname);
}
Or as noted in the comments, as the attributes has a default value of false you don't have to explicitly set them to that
function OnceNamedOne() {
Object.defineProperty(this, 'firstname', {value : 'John'});
Object.defineProperty(this, 'lastname', {value : 'Dow'});
Object.defineProperty(this, 'fullname', {value : this.firstname + ' ' + this.lastname});
}
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