Category: coding

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JS rounding numbers

I have a requirement to be able to round numbers to either a whole number or to a specified number of decimal places….

Every now and then i find myself looking over my current solution to a problem when applying it in a new project. In this case it was very simple statistics and mean values.

For example:

const dec = [2, 678, 65.67467, 10.5452453453, 1, 0];
// Required outcome to 3 decimal places
// 2, 678, 65.675, 10.545, 1, 0

// Or to 2 decimal places
// 2, 678, 65.67, 10.55, 1, 0

My solution:

const round = (n, decimal = 2) => {
    return Math.round(n * Math.pow(10, decimal)) / Math.pow(10, decimal);
};
// Quick test
dec.forEach(n => {
console.log(round(n, 3));
});

dec.forEach(n => {
console.log(round(n));
});

As an aside: I need to have a set of numbers rounded and set with 2 fixed decimal places. So the same data set would be:

const dec = [2, 678, 65.67467, 10.5452453453, 1, 0];

// Required response would be
// 2.00, 678.00, 65.67, 10.55, 1.00, 0.00

There is the Number.toFixed() method

dec.forEach(n => console.log(n.toFixed(2)));
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Finding, replacing, deleting and adding to a nested collection

Problem: I have an object that has a field call modules that is and array of activities. Activities is itself a complex and many nested object. I need to hunt for activities by their IDs and replace, delete or insert between existing objects

// Replace object in collection
Object.keys(data.modules).forEach(modKey => {
  Object.keys(data.modules[modKey].activities).forEach(activityKey => {
    if (data.modules[modKey].activities[activityKey].id === newActivity.id) {
      data.modules[modKey].activities.splice(activityKey, 1, newActivity);
    }
  });
});
// Remove object in collection
Object.keys(data.modules).forEach(modKey => {
  Object.keys(data.modules[modKey].activities).forEach(activityKey => {
    if (
      data.modules[modKey].activities[activityKey] &&
      data.modules[modKey].activities[activityKey].id === newActivity.id
    ) {
      data.modules[modKey].activities.splice(activityKey, 1);
    }
  });
});
// Insert object at index
const moudleIndex = 0;
const activityIndex = 2;

Object.keys(data.modules).forEach(modKey => {
  if (modKey == moudleIndex) {
    Object.keys(data.modules[modKey].activities).forEach(activityKey => {
      if (activityKey == activityIndex) {
        data.modules[modKey].activities.splice(activityKey, 0, newActivity);
      }
    });
  }
});

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REGEX Examples with explanations

A string 24 characters in length and only with hexadecimal letters and numbers

Example use: In MongoDb the unique id’s (ObjectId)

The string must be 24 characters long. ^ Starts of string or start of line, $ end of string or line; both dependent on the “multi-line mode”

/^{24}$/

Hexadecimal uses only the letters “a to f” and the number “0 to 9”

/^[a-f0-9]{24}$/

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REGEX 2

Okay in the previous post we had found the “find” tool and realised we can do so much more with it using regular expressions (regEx).

To recap a regEx is

“a sequence of symbols and characters expressing a string or pattern to be searched for within a longer piece of text.”

\d = a character 0 to 9

\w = any character a to Z and 0 to 9

\s =  whitespace

Example:

\d\d\d will (using the find tool in your text editor) will highlight groups of 3 numbers in a string

\w\w\w\w\w will highlight groups of 5 characters

Notice how \w\w\w included numbers and letters

\s\s will highlight double spaces

Lets look for words that have only 4 characters.

A 4 letter word can be described as,

“a space followed by any 4 characters, followed by a space”

\s\w\w\w\w\s

Which can be rewritten as

\s\w{4}\s

But that will also include numbers. To ignore numbers

\s\w{4}[a-z]\s

Not quite there, if you are playing along you will notice that we are highlighting 4 letter words and the space before and after. What we need is to set boundaries.

\b\w{4}[a-z]\b

\b is a boundary, there are a few but for now lets stay with ‘spaces’. So with that you can find all four letter words

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REGEX 1

Part 1 of understanding regular expressions (regEx).

RegEx is not just useful when writing code ( across different languages they are broadly similar) but I have found knowing a bit allows me to quickly become a “power user” when using the find replace functions in text editors like VSCode and PHPStorm.

If you are using VSCode bring up the “find” box and have a look for the icon .*

So instead of just searching for a text string you can quickly scan more accurately.

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PHP7 The Null Coalesce Operator

This is a simple and quick to describe, it will even save you a bunch of typing.

Before PHP 7

$name = isset($_POST['name']) ? $_POST['name']  : 'Default name';

Now with PHP 7

$name = $_POST['name'] ?? 'Default name';

Soooo much better

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What they never tell you about GitHub

GitHub is brilliant…. There are loads of tutorials, video and articles out there, recently I’ve spent time filling gaps in my Git version control knowledge and something struck me as odd. Every tutorial should make it clear right from the start and reminders throughout their presentations that you

DO NOT STORE PASSWORDS, KEYS, USERNAMES, CREDENTIALS, ETC. ON GIT HUB

Why?

Because there are bastards out there who are scanning git repositories for anything that could help access secured areas or consume resources they should not.

Git does scan your repo’s and will warn you but its not in real time so be warned. Still not convinced? The image is of a free Amazon Web Service account that was set up as a learning exercise the keys where saved in a Git Repo and over the course of 3 days a free account had racked up nearly $10,000US .

What can you do, if you accidentally commit a password, key, etc? Delete the branch? Roll back?

No!

The best advice and this is also given by Git themselves is to consider your data compromised and your accounts that use the data hacked. Once again, rolling back and deleting does not work.

So reset your passwords/key etc and don’t just add a 1 at the end or swap out vowels for 12345.

How do you manage password and environment values?

Have a Google for git .gitignore or visit dotIgnore on GitHub

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JavaScript fetch()

In a previous post I was refreshing my memory with vanilla JavaScript  after years of jQuery-ing, especially AJAX request and the

XMLHttpRequest()

My eyes rolled when I was reading more about it then  I found fetch()  ( I know its been about since 2015 and now almost universally adopted).

Fetch does what XMLHttpRequest does but in a more elegant way and DOES NOT need additional libraries as it is bundled with JavaScript. It also makes use of “promises” .

const url = "https://randomuser.me/api/?results=10";

fetch(url)
.then(function(response) {
 return response.json();
})
.then(function(data) {
 console.log(data.results);
})
.catch(function() {
 console.log("Booo");
});

The above code queries the URL, then parses the string as JSON, then does something with the data.

It also catches errors.

Good eh?

Its looks to be easy to expand and do all manner of fetching. For example submitting a form

var form = new FormData(commentForm);
fetch( url, { method: "POST", body: form })

You can then chain .then() promises to get the desired outcomes.

For more information

A quick introduction video from Google

From Google Working with the Fetch API

Jake Archibald’s post Thats so Fetch

Scotch post The Fetch API

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strpos() not working?

PHP strpos() not working as expected? It could be a  “non-strict” comparison problem.

When using strpos() to determine whether a substring exists within a string the  results can be misleading: Remember FALSE == 0?

Consider the following:

$quote = 'Dave rocks';
 
if (strpos($quote, 'Dave')) {
    echo 'Dave is awesome.';
} else {
    echo 'Dave is not awesome.';
}

strpos() Returns position is 0 ( zero ) that is evaluated as FALSE so, “Dave is not awesome”.

Much better. In this case adding the strict comparison === ( 3 equals ) to the “if” statement asks if strpos() returns a number and  is not strictly FALSE. So, “Dave is awesome”

$quote = 'Dave rocks';
 
if (strpos($quote, 'Dave') !== FALSE) {
    echo 'Dave is awesome.';
} else {
    echo 'Dave is not awesome.';
}

For more see PHP.net