DEV Community: pampapati

JavaScript for...in iteration

pampapati — Sun, 03 Jul 2022 09:45:49 +0000

In this post will try to showcase different ways for the iterations.

using forEach
using for...of
using for...in
using for

let list = [1,2];
list.newCustomElement = true;

list.forEach( (item)=>{
console.log(item);
});

//Output 
1
2


for(let item of list){
console.log("using of",item);
}

//Output 
"using of", 1
"using of", 2

for(let item in list){
console.log("using in",item);
}

//Output 
"using in", "0"
"using in", "1"
"using in", "newCustomElement"



for(let i=0;i<list.length;i++){
console.log(list[i]);
}
//Output 
1
2

Don't use for...in to iterate the array , if the order is important

Will see another example for better understanding of for..in


const Employee= {
    name: 'John',
    dept: 'IT',
    age: 29
}


for ( let key in Employee) {
    console.log(key);
}

Output:
"name"
"dept"
"age"

for ( let key in Employee) {
    console.log('key: ',key,' value:', Employee[key]);
}

Output:
"key: ", "name", " value:", "John"
"key: ", "dept", " value:", "IT"
"key: ", "age", " value:", 29

In above example for...in is used to print properties on Employee object.

First for loop in above example will showcase that object keys are printed using iterator key, it wont print the values of property.

Second for loop in above example will showcase how to print keys and the values of property.

Flat Nested Array: JavaScript

pampapati — Sun, 26 Jun 2022 08:32:48 +0000

Flat nested array without using built-in methods. Recursive program example

const arr = [1,2,[3,4],5,[6,[7,8],9],10];

function flatArray(input,output){   
  input.forEach( (value)=>{    
    if(typeof value== 'object'){
      flatArray(value,output);
    }else{
      output.push(value);
    }    
  });
  return output;  
}

console.log(flatArray(arr,[]));

How to create JavaScript Objects

pampapati — Sun, 26 Jun 2022 08:19:10 +0000

-using {}

-using new Object()

-using Object.create()

-using Object.assign()

-using ES6 Class

Object Creation Using ES6 Class:

class Employee{
   constructor(name,dept){
       this.name = name;
       this.dept = dept;
   }
}

const firstEmployee = new Employee('Pavan','IT');
console.log(firstEmployee);

Output // 
{
name: 'Pavan', 
dept: 'IT'
}

Format Array : JavaScript

pampapati — Sun, 26 Jun 2022 07:42:47 +0000

Input:
[ { x: 'a', order: 10}, { x: 'a', order: 3}, { x: 'a', order: 4}, { x: 'b', order: 3}, { x: 'b', order: 2}, { x: 'b', order: 1} ]

Output :
{ “a":[{"x":"a","order":10},{"x":"a","order":3},{"x":"a","order":4}], “b":[{"x":"b","order":3},{"x":"b","order":2},{"x":"b","order":1}] }

Solution:

const arr = [
  { x: 'a', order: 10},
  { x: 'a', order: 3},
  { x: 'a', order: 4},
  { x: 'b', order: 3},
  { x: 'b', order: 2},
  { x: 'b', order: 1}
];

function formatArray(input){
  output = {};
  input.forEach( (value)=>{
    const xValue = value.x;
    if(Object.keys(output).includes(xValue+'')){
      output[xValue].push(value);
    }else{
      output[xValue] = [value];
    }    
  });
  return output;
}

console.log("output",formatArray(arr));