How to use interface and default parameters together?

Question

Code below:

enum Type { digit=1, alpha=2, alnum=3 }
enum Transform{uppercase=1,lowercase}
    interface Options {
    type: Type;
    length: number;
    min: number;
    max: number;
    uppercase: boolean;
    lowercase: boolean;
    transform: Transform;
    valueChange: (element:Object,value:string) => string;
 }
 class InputFilter {
    constructor(private options: Options, private element: Object) {
    }
}

I wanna to make options not only have interface,also have defaulte value,just like this:

 options = {
    "type": "alnum",
    "length": null,
    "min": 0,
    "max": Infinity,
    "uppercase": true,
    "lowercase": true,
    "transform": null,
    "valueChange": function(element, value) {}
};

How can I do that?

Answer 1

You will need to create a factory method or function somewhere that will create an object with the default values that conforms to your interface.

Here's an example:

function createOptionsWithDefaultValues(): Options {
    return {
        type: Type.alnum,
        length: null,
        min: 0,
        max: Infinity,
        uppercase: true,
        lowercase: true,
        transform: null,
        valueChange: function(element, value) {
            return null;
        }
     };
 }

 let options = createOptionsWithDefaultValues();
 // use options...