README.md

javascript-practice

Repo for JavaScript exercises from books e.g. Eloquent JavaScript, JavaScript and JQuery), code challenges or code mastery sites (e.g. CodeWars, LeetCode, Interview Cake).

All functions have been developed with full TDD using the (Jest)[https://jestjs.io/] testing library.

Running the tests Node.js must be installed.

First, clone this repository and install dependencies:

npm install

To run the tests:

npm test

JavaScript Basics and Handy Functions for Puzzles

falsey value example

[0, null, undefined, false, ""]

loops

for loop

for (let i = 0; i < arr.length; i++) {
  // do something with arr[i]
}

forEach

• Available on arrays only
• Access every item 1 by 1
• Very versatile, do whatever you want with each item in an array

const arr = ["foo", "bar", "baz"];

arr.forEach(function(item) {
  // do something with item
});

functions

Regex

test returns boolean

  // regex for Manchester postcodes
  const re = new RegExp('^M\\d');
  return re.test(person.address.postCode);

search returns position of the match

var str = "Visit Tokyo!";
var n = str.search("Tokyo"); // returns 6

replace replaces the first string argument with the second

var str = "Visit Sydney!";
var res = str.replace("Sydney", "Hong Kong");

filter

• Available on arrays only
• Access every item 1 by 1
• Used to select only specific items from an array
• Return true to keep an item, false to reject
• Remember to save the new array in a variable

const filtered = nums.filter((n) => Number.isInteger(n));

map

return users.map(function (user) {
    return user.data.city.displayName;
  });
// or as an arrow function to a variable 
  const newArr = users.map((user) => user.data.city.displayName);

reduce - returns the total of the values in the array

const data = [5, 10, 15, 20, 25];
const res = data.reduce((total,currentValue) => total + currentValue);

// alternative syntax
// also assigning an initial value of 29 (usually takes the first array item)
data = [11, 21, 19, 18, 46]
const reducer = (accumulator, currentValue) => accumulator + currentValue
result = data.reduce(reducer, 29);