An Interface example for TypeScript

interface-example.ts

interface IFunc {
	(n: number[]): number;
}

interface IOperations {
	add: IFunc;
	sub: IFunc;
	mul: IFunc;
	div: IFunc;
}

interface IClass {
	operations: IOperations;
	perform(operator: string, ...args: number[]): number;
}

class Calc implements IClass {
	operations: IOperations;
	constructor(operations: IOperations) {
		this.operations = operations;
	}
	perform(operator: string, ...args: number[]): number {
		switch (operator) {
			case '+': return this.operations.add(args);
			case '-': return this.operations.sub(args);
			case '*': return this.operations.mul(args);
			case '/': return this.operations.div(args);
		}
	}
}

let c = new Calc({
	add: (n: number[]): number => n.reduce((p: number, c: number): number => p + c, 0),
	sub: (n: number[]): number => n.slice(1).reduce((p: number, c: number): number => p - c, n[0]),
	mul: (n: number[]): number => n.reduce((p: number, c: number): number => p * c, 1),
	div: (n: number[]): number => n.slice(1).reduce((p: number, c: number): number => p / c, n[0]),
})

alert(c.perform('+', 10, 21, 37, 42)); // 10 + 21 + 37 + 42 = 110 
alert(c.perform('-', 97, 2, 13, 25)); // 97 - 2 - 13 - 25 = -137
alert(c.perform('*', 48, 1, 34, 72)); // 48 * 1 * 34 * 72 = 117504
alert(c.perform('/', 81, 3, 4)); // 81 / 3 / 4 = 6.75