1. Variables

The nullish coalescing operator (??) is a logical operator that returns its right-hand side operand when its left-hand side operand is null or undefined and otherwise returns its left-hand side operand. We can use this to set default values, for example when we receive a list that has not been set to an array yet:

const bookList = receivedBooks ?? [];

2. Parameters

We could use the null coalescing operator to set defaults for variables in functions but there is a better way, default parameters:

function calculateArea(width, height = 100) {
    return width * height;
}

const area = calculateArea(50);
console.log(area); // 5000

3. Objects

We can also give default value once we destructure object properties. ES6 destructuring default values only kick in if the value is undefined.

const rectangle = { height: 400 };
const { height = 750, width = 500 } = rectangle;
console.log(height); // 400 - comes from rectangle object
console.log(width);  // 500 - fallback to default

Links

• nullish coalescing operator (??)
• default parameters