Optional.md

Optional and why?

Optional is a construct to avoid explicit null/undefined references. In Typescript this construct is not explicitly needed anymore because we have optional references within the language. Which in my opinion is the better construct. However in javascript we don´t.

So what happens here

typescript

• a.b.c if be defaults to null, results in a null pointer error
• a?.b?.c howver returns a null

The first construct usually if no optional references are given, must be resulved by a chain of boolean if conditions.

if('undefined' != typeof a  && null != a && 'undefined' != typeof a.b && null != typeof a.b) {
    return a.b.c;
} else {
    return null;
}

Now you can see, whenever we have such construct and no direct language support there must be an easier way, and there Optional and Config come into play.

if(Optional.fromNullable(myVar).isAbsent()) {
    //do something
}

The same goes for exists checks:

let opt = Optional.fromNullable(myVar);
if(Optional.fromNullable(myVar).isPresent()) {
    //do something
    let theValue = opt.value; //lets fetch the value
}

Also as convenience you now have an easier way to check for existence in nested structures

        let myStruct = {
            data: {
                value: 1,
                value2: Optional.absent,
                value4: Optional.fromNullable(1)
            },
            data2: [
                {booga: "hello"},
                "hello2"
            ]
        };
        
        let opt = Optional.fromNullable(myStruct);
        opt.getIf("data", "value3").isAbsent(); // returns true
        opt.getIf("data", "value4").value; //returns 1
        opt.getIf("data2[0]", "booga").value; //returns "hello"
        opt.getIf("data2[1]").value; //returns "hello2"
                

• or in a typesafe manner:

    opt.resolve(item => item.data.value3).isAbsent()
    opt.resolve(item => item.data.value4).value

if the data cannot be resolved optional is returnd in a state of absent

As you can see, it is very easy to fetch cascaded data. The result of getIf always is another optional. To access the value of the optional, simply use the .value property.

Optional is readonly and sideffect free.