Typescript: If am defining a variable type as interface type am getting error

Question

In the below code I am getting an error in statement (emp:IEmployee= { FirstName: "Saurabh", LastName: "Vats" };) when am trying to define a variable as interface type. Why is TypeScript is giving me error here?

class Greeter {
    element: HTMLElement;
    span: HTMLElement;
    timerToken: number;
    constructor(element: HTMLElement) {
        this.element = element;
        this.element.innerHTML += "The time is: ";
        this.span = document.createElement('span');
        this.element.appendChild(this.span);
        this.span.innerText = new Date().toUTCString();
    }

    start() {
        this.timerToken = setInterval(() => this.span.innerHTML = new Date().toUTCString(), 500);
    }

    stop() {
        clearTimeout(this.timerToken);
    }

    print(employee: IEmployee) {
        console.log(employee.FirstName + employee.LastName);

    }

}

interface IEmployee {
    FirstName: string;
    LastName: string;
}
window.onload = () => {
    var el = document.getElementById('content');
    var greeter = new Greeter(el);
    greeter.start();
    emp:IEmployee= { FirstName: "Saurabh", LastName: "Vats" };
    greeter.print(emp);

};

It does not just give you "an error". It gives you a specific error message. — str
– str, Commented Aug 5, 2016 at 5:34
That should have been in the question. Also, do not rephrase the error message, just add it exactly the way you get it. — str
– str, Commented Aug 5, 2016 at 5:42

Andrew Shepherd · Accepted Answer · 2016-08-05 06:00:48Z

2

You're just missing a keyword.

This is incorrect:

emp:IEmployee= { FirstName: "Saurabh", LastName: "Vats" };

It should be:

let emp:IEmployee= { FirstName: "Saurabh", LastName: "Vats" };

But what if, for some reason, you wanted to make it a global variable?

In javascript, if you had written:

emp = { FirstName: "Saurabh", LastName: "Vats" };

You would actually be adding this to the window object.

You can still do this in typescript, you just have to be explicit about it:

interface Window {
    emp:IEmployee;
}

window.onload = () => {
     var el = document.getElementById('content');
     var greeter = new Greeter(el);
     greeter.start();
     window.emp = { FirstName: "Saurabh", LastName: "Vats" };
     greeter.print(emp);
};

edited Aug 5, 2016 at 6:00

answered Aug 5, 2016 at 5:34

Andrew Shepherd

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6 Comments

saurabh vats Over a year ago

let is working fine but it creates a variable in local scope, if I am not giving the let keyword I was expecting it to create a global variable but instead I am getting error

user663031 Over a year ago

@saurabhvats Why on earth would you want to create a global variable, and why on earth would you imagine in an ES6 world that you could do that that way?

saurabh vats Over a year ago

am new to typescript so I thought that as javascript creates global variable when you dont specify the var keyword, I thought typescript would behave in the same manner. its fine if it throws the error for variable without 'let' keyword

Andrew Shepherd Over a year ago

@saurabhvats I extended my question to say how you would create it as a global variable. (Not that I'm saying it's a good idea).

saurabh vats Over a year ago

just noticed while defining global variable also am unable to say "window.emp:IEmployee" rather I have to say window.emp ?

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