A guide on creating a concatenation function using TypeScript

Question

A guide on creating a concatenation function using TypeScript

Looking for a way in Typescript to define an interface Calculator that allows for concatenation capabilities?

interface Calculator {
    ...
}
 
let calcu: Calculator;
calcu(2).multiply(5).add(1)

I attempted the following:

interface Calculator {
  (num: number): Calculator;
  multiply(num: number): Calculator;
  add(num: number): Calculator;
}

Encountered an error stating that calcu is not instantiated:

Variable 'calcu' is used before being assigned

My question now is how can I define the interface Calculator and successfully instantiate calcu.

typescript function concatenation

Answer 1

Answer №1

Interfaces serve to outline the structure of something; it is advisable to create a class that can be initialized with new.

For example:

class Calculator
{
    constructor(public num: number) { }
    multiply(num: number)
    {
        this.num *= num;

        return this;
    }
    add(num: number)
    {
        this.num += num;

        return this;
    }
}

const calcu = new Calculator(2);
calcu.multiply(5).add(1);

console.log(calcu.num);

If you prefer to interact directly with the interface and plain objects, it is possible but quite cumbersome, as shown below:

const calcu: Calculator = (() =>
{
    let value;

    const fun = function (num: number)
    {
        value = num;

        return fun;
    };
    fun['multiply'] = (num: number) =>
    {
        value *= num;
        return fun;
    };
    fun['add'] = (num: number) =>
    {
        value += num;
        return fun;
    };

    return fun;
})();

calcu(2).multiply(5).add(1);

(It may also be beneficial to define a function that reveals the internal value, as it is currently concealed.)

Answer 2

Interfaces serve to outline the structure of something; it is advisable to create a class that can be initialized with new.

For example:

class Calculator
{
    constructor(public num: number) { }
    multiply(num: number)
    {
        this.num *= num;

        return this;
    }
    add(num: number)
    {
        this.num += num;

        return this;
    }
}

const calcu = new Calculator(2);
calcu.multiply(5).add(1);

console.log(calcu.num);

If you prefer to interact directly with the interface and plain objects, it is possible but quite cumbersome, as shown below:

const calcu: Calculator = (() =>
{
    let value;

    const fun = function (num: number)
    {
        value = num;

        return fun;
    };
    fun['multiply'] = (num: number) =>
    {
        value *= num;
        return fun;
    };
    fun['add'] = (num: number) =>
    {
        value += num;
        return fun;
    };

    return fun;
})();

calcu(2).multiply(5).add(1);

(It may also be beneficial to define a function that reveals the internal value, as it is currently concealed.)

A guide on creating a concatenation function using TypeScript

Answer №1

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