Guard Clauses

Guard clauses reject invalid input before the main work starts.

guards.ts

function priceLabel(cents: number): string {
    if (cents < 0) {
        return "invalid";
    }
    if (cents === 0) {
        return "free";
    }
    return `$${(cents / 100).toFixed(2)}`;
}

const cents: number = ;
const label: string = priceLabel(cents);

console.log(`price=${label}`);

function priceLabel(cents: number): string {
    if (cents < 0) {
        return "invalid";
    }
    if (cents === 0) {
        return "free";
    }
    return `$${(cents / 100).toFixed(2)}`;
}

const cents: number = ;
const label: string = priceLabel(cents);

console.log(`price=${label}`);

function priceLabel(cents: number): string {
    if (cents < 0) {
        return "invalid";
    }
    if (cents === 0) {
        return "free";
    }
    return `$${(cents / 100).toFixed(2)}`;
}

const cents: number = ;
const label: string = priceLabel(cents);

console.log(`price=${label}`);

guard clause A guard clause checks a requirement early and returns or throws before the rest of the function runs.