DEV Community: Mohd Ahshan Danish

Backup, Empty and Restore CRONTAB

Mohd Ahshan Danish — Fri, 23 Feb 2024 05:38:26 +0000

It is always very challenging to stop and restart crontab. Below are the commands to backup and restore crontab 😀

flatMap vs map in Array

Mohd Ahshan Danish — Sun, 21 Jan 2024 13:51:56 +0000

flatMap: It is identical to a map() followed by a flat() of depth 1 (arr.map(...args).flat()), but slightly more efficient than calling those two methods separately.

let LIST = [1,2,3];
let processedLst = LIST.flatMap((route) => {
    return [route, route];
  }).filter(Boolean);
console.log(processedLst)
// [ 1, 1, 2, 2, 3, 3 ]

map:

let LIST = [1,2,3];
let processedLst = LIST.map((route) => {
    return [route, route];
  }).filter(Boolean);
console.log(processedLst)
//[ [ 1, 1 ], [ 2, 2 ], [ 3, 3 ] ]

flat():

processedLst.flat()
//[ 1, 1, 2, 2, 3, 3 ]

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Default CSS for Img

Mohd Ahshan Danish — Sat, 23 Dec 2023 17:16:04 +0000

Default css for rendering image properly.

max-width:100%
(container size is smaller then image)
hight:auto
(maintain aspect ration)
vertical-align:middle
(image will not have empty space in bottom)
front-style:italic
(alt text)
background-repeat:no repeat;
background-size : cover
(low quality image)
shape-margin: 0.5rem
(margin)

Solution for 'await is only valid in async functions'

Mohd Ahshan Danish — Fri, 22 Dec 2023 17:07:40 +0000

We can only execute await inside an async function. If you try to use await without an async function, it will result in an error.

Solution: One good option to address this issue is by using IIFE (Immediately Invoked Function Expression).

(async function(){
    let a = await testSleep();
    console.log(a);
   let b = await testSleep();
    console.log(b);
})();

Problem with for in

Mohd Ahshan Danish — Sun, 17 Dec 2023 08:10:44 +0000

We have an instance of Obj1. This instance has attributes name and age. When we print obj1, it returns the instance properties of the object, only name and not the age. However, Obj1's prototype also has a property age, and that property is not directly accessible through the instance of obj1.

function obj1(){
    this.name= "myName";
}
obj1.prototype.age = 10;
const i = new obj1();
console.error(i);
// obj1 { name: 'myName' }

but when we do for in.

for(let prop in i){
   console.error(prop); 
}
// name and age both property is present

Problem with for in is that it returns not only instance property of object but also all properties it inherit through prototype.

Solution: we can use hasOwnProperty for instance property.

for(let prop in i){
    if(i.hasOwnProperty(prop)) console.error(prop); 
}

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groupBy in JS

Mohd Ahshan Danish — Sun, 17 Dec 2023 04:08:30 +0000

Object.groupBy is a recently released method in JavaScript and it is a useful function for manipulating objects and collections.

Note: We can pass a complex function as a parameter to the groupBy method for manipulation.

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toSorted() vs sort()

Mohd Ahshan Danish — Fri, 15 Dec 2023 01:12:21 +0000

toSorted() is a recently released method that creates a copy of the existing array and returns a new array. Unlike the sort() function, toSorted() does not alter the original array.

//  sort
const array1 = [ { name: "k", age: 12 } ,{ name: "a", age: 14 }, { name: "b", age: 14 }, { name: "c", age: 13 }, { name: "d", age: 13 }, { name: "e", age: 13 }, { name: "f", age: 13 }, { name: "g", age: 13 }, { name: "h", age: 13 }, { name: "i", age: 12 }, { name: "j", age: 12 }, ]

array1.**sort**( (a,b) => a.age - b.age)
console.error(array1)

output
[ { name: 'k', age: 12 }, { name: 'i', age: 12 }, { name: 'j', age: 12 }, { name: 'c', age: 13 }, { name: 'd', age: 13 }, { name: 'e', age: 13 }, { name: 'f', age: 13 }, { name: 'g', age: 13 }, { name: 'h', age: 13 }, { name: 'a', age: 14 }, { name: 'b', age: 14 } ]

toSorted:

output

Here you can see the original array has not been modified.

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null !== undefined

Mohd Ahshan Danish — Wed, 13 Dec 2023 00:49:30 +0000

I have noticed that many developers struggle with the appropriate use of "null" and "undefined" in JavaScript.

"Null" refers to the absence of any object value. It is primarily used when an object is not present.

console.log(typeof null) // 'object'

"Undefined" is used when something is not defined. If any attribute in an API is missing, it will be considered as "undefined".

let i;
console.error(typeof i) // undefined

Note: It is important to always compare attribute values with "undefined" when processing API responses.

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Function Scope in JS

Mohd Ahshan Danish — Tue, 12 Dec 2023 02:05:01 +0000

Functions in Javascript run in the scope they are defined, not in the scope they are executed.

var baz;
(function() {
  baz = function() {
    return foo * bar;
  };
  var foo = 20;
  var bar = 2;
})();

console.error(baz());

//output: 40

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SFTP vs FTPS

Mohd Ahshan Danish — Tue, 12 Dec 2023 01:14:46 +0000

Recently, I have finished working on an SFTP file transfer implementation. While learning and exploring both SFTP and FTPS protocols,I discovered that we often get confused between SFTP and FTPS.

FTP and SFTP enable secure file access, but they differ in certain ways.

SFTP is secure, fully encrypted, and securely integrated with firewalls.

FTPS, on the other hand, add a layer of encryption using SSL or TLS. It offers faster file transfer compared to SFTP.

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Indent the output of 𝐉𝐒𝐎𝐍.𝐬𝐭𝐫𝐢𝐧𝐠𝐢𝐟𝐲

Mohd Ahshan Danish — Tue, 12 Dec 2023 00:36:01 +0000

While working with the Oracle Field Service plugin in Javascript, I have observed that many developers use 𝐜𝐨𝐧𝐬𝐨𝐥𝐞.𝐥𝐨𝐠(𝐉𝐒𝐎𝐍.𝐬𝐭𝐫𝐢𝐧𝐠𝐢𝐟𝐲()) and struggle with the structure of objects on the console. The 𝐉𝐒𝐎𝐍.𝐬𝐭𝐫𝐢𝐧𝐠𝐢𝐟𝐲() method provides an option to properly indent the output on the console for debugging, which can be very helpful for understanding the structure of the objects.

// JSON.stringify 
const person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"};
console.log(JSON.stringify(person));
/*
output
  {"firstName":"John","lastName":"Doe","age":50,"eyeColor":"blue"}
*/

// Indent the output with one space
console.log(JSON.stringify(person,null,"\t"));
/*
output
  {
    "firstName": "John",
    "lastName": "Doe",
    "age": 50,
    "eyeColor": "blue"
}
*/

I will be posting tricks I have been using in my journey.

So follow me on LinkedIn.