Is there an elegant way to set a class property only once?

Question

In TypeScript, while in a class, is there an elegant way to set a value only once? In other words, is there an equivalent of setting a value as readonly after giving it a value?

For example:

class FooExample {
    public fixedValue: string;

    public setFixedValue(value: string): void {
        if (!this.fixedValue) {
            // this value should be immutable
            this.fixedValue = value;
        }
    }
}

I am not looking for a getter, because the class property could be changed within the class itself.

Answer 1

After reading the suggested answers and doing my own research I believe I have found the most elegant solution. You first define the value as an Object and then freeze() the Object after populating the related property.

class FooExample {
    public fixedValue = {
        value: '';
    };

    public setFixedValue(value: string): void {
        if (!Object.isFrozen(this.fixedValue)) {
            this.fixedValue.value = value;
            Object.freeze(this.fixedValue);
        }
    }
}