Default parameters: basics

Default parameters make function parameters more flexible

define it using an assignment to the parameter function(param=1){}

let aNumber = (int) => int; assert.equal(aNumber(), 0);

it is used when undefined is passed

let aNumber = (int = 23) => int; const param = 42; assert.equal(aNumber(param), 23);

it is not used when a value is given

function xhr() { return method; } assert.equal(xhr('POST'), 'POST');

it is evaluated at run time

let defaultValue; function xhr(method = `value: ${defaultValue}`) { return method; } assert.equal(xhr(), 'value: 42');

it can also be a function

const defaultValue = 0; function fn(value = defaultValue()) { return value; } assert.equal(fn(), 'defaultValue');

Required Knowledge

• basics (Template strings)
• basics (Arrow functions)
• `let` declaration (Block scope)

Related Katas

Default parameters

• basics

Difficulty Level

BEGINNER

First Published

30 June 2015

Stats

5 tests to solve