Node.js
Summary - Functions
Combine arrow functions, default and rest to write a math helper.
Summary - Functions
In this group you saw five aspects of functions: definition (declaration and expression), returning values with return, the short arrow function form, default parameters for fallback values, and rest parameters for variable arguments.
You can combine these to write flexible helper functions. A 'calculator helper', for example: written as an arrow function, taking a default rate and processing as many numbers as you want with a rest parameter.
In the final task you will write a function that computes an average. It will take a variable number of values with a rest parameter and return their average. You will use arrow functions and reduce together.
Exercise Calculator helper
Define an arrow function named apply: const apply = (rate = 10, ...nums) => nums.reduce((sum, n) => sum + n * rate / 100, 0);. Print the result of apply(20, 100, 200) (100*20/100 + 200*20/100 = 60) with console.log.
Show example solution
const apply = (rate = 10, ...nums) =>
nums.reduce((sum, n) => sum + n * rate / 100, 0);
console.log(apply(20, 100, 200));
Exercise Compute the average
Define an arrow function named average: const average = (...nums) => nums.reduce((sum, n) => sum + n, 0) / nums.length;. Print the result of average(10, 20, 30, 40) (100 / 4 = 25) with console.log.
Show example solution
const average = (...nums) =>
nums.reduce((sum, n) => sum + n, 0) / nums.length;
console.log(average(10, 20, 30, 40));
Test yourself
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Match the concepts
- function greet
- Declaration
- return n * 2
- Returning a value
- (a) => a * 2
- Arrow function
- rate = 18
- Default parameter
- ...nums
- Rest parameter
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What does the calculator helper take?
- A single number
- Two fixed parameters
- Only an array
- A default rate and rest numbers
Show answer
A default rate and rest numbers — a default rate plus rest numbers gives a flexible helper.
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Arrow with a default parameter
const greet = (name = ____) => 'Merhaba ' + name;
Show answer
const greet = (name = 'Misafir') => 'Merhaba ' + name;
Next lesson: What are callbacks?
