Error instantiating Typescript Class (Error not a constructor)

Question

I am new to TypeScript and am having trouble with basic class instantiation.

I have a namespace RecordsService with class Record declared inside of it. I want to be able to create Records within RecordsService, then access them via public methods from other methods and such.

export namespace RecordsService {

    let records: Array<Record> = new Array();

    function init () {
        let record1 = new Record(new Date(), 1);
    }
    init();

    export function getAllRecords() {
        return records;
    }

    class Record {

        constructor (public date: Date, public id: number) {
            this.date = date;
            this.id = id;
        }
    }
}

The above doesn't throw any transpiling error but when ran I get a console error with the below

TypeError: Record is not a constructor(…)

line that errors is let record1 = new Record(new Date(), 1); How can I create a new Record in this case?

Plunker, view console log to see error: https://plnkr.co/edit/FNk8b1ZwA5HL3I7wAnTq?p=preview

Nitzan Tomer · Accepted Answer · 2016-07-11 11:52:23Z

You need to move your Record class to be above the init function:

class Record {
    constructor (public date: Date, public id: number) {
        this.date = date;
        this.id = id;
    }
}

let records: Array<Record> = new Array();

function init () {
    let record1 = new Record(new Date(), 1);
}
init();

Or call the init function after the definition of Record:

let records: Array<Record> = new Array();

function init () {
    let record1 = new Record(new Date(), 1);
}

export function getAllRecords() {
    return records;
}

class Record {
    constructor (public date: Date, public id: number) {
        this.date = date;
        this.id = id;
    }
}

init();

The reason why this happens is that javascript is an interpreted language, the interpreter parses the code line after the other, and so it reaches the init() part (in you original code) before it interpreted the Record class.

The content of the init function isn't interpreted until you execute the function which is why it's safe to have it before the class definition and just execute it afterwards.

Also, if you're doing this:

constructor (public date: Date, public id: number)

Then there's no need to do this:

this.date = date;
this.id = id;

It's either:

class Record {
    constructor (public date: Date, public id: number) {}
}

Or

class Record {
    public date: Date;
    public id: number;

    constructor (date: Date, id: number) {
        this.date = date;
        this.id = id;
    }
}

Thanks, love when errors are silly things I know but didn't think of

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