Few Javascript or JQuery Tricks for array and operators

 1) Empty an array

var arr = [10 , 20 , 30 ];
arr.length = 0; // arr will be equal to [].

2) Truncate an array using length

Like the previous example of emptying an array, we truncate it using the length property.

var arr = [10, 20, 30, 40, 50, 60, 70, 80, 90];
arr.length = 4; // arr will be equal to [10, 20, 30, 40].

As a bonus, if you set the array length to a higher value, the length will be changed and new items will be added with undefined as a value. The array length is not a read only property.

arr.length = 10; // the new array length is 10
arr[arr.length - 1] ; // arr [10, 20, 30, 40, 50, 60, 70, 80, 90, undefined];

3)Use logical AND/ OR for conditions

var foo = 10;
foo == 10 && doSomething(); // is the same thing as if (foo == 10) doSomething();
foo == 5 || doSomething(); // is the same thing as if (foo != 5) doSomething();

4) Comma operator

var a = 10;
var b = ( a++, 99 );
console.log(a);  // a will be equal to 10
console.log(b);  // b is equal to 99

5) Swap variables

let v1 = 'value 1';
let v2 = 'value 2';

[v1,v2] = [v2, v1];
console.log(v1, v2);

Calculate date difference using JQuery

Simple way to get days between 2 dates...

var date1 = new Date("12/13/2021"); // MM/dd/yyyy var date2 = new Date("01/01/2021"); // MM/dd/yyyy // date1 - date2 returns difference in milliseconds var diff = new Date(date1 - date2); // get days var days = diff/1000/60/60/24; console.log(days)

Cheat Sheet - CSS, JQuery Selectors and Filters

*	All elements.
element	Basic selector defined by the elements name. IE – the <p> tag.
.class	Elements specified by a specific class attribute.
#id	Elements specified by the specific ID number.
selector1, selector2	Elements that match more than one selector.
:first	First element from the selection.
:last	Last element from the selection.
:even	Even index selection.
:odd	Odd index selection.
:not(selector)	Everything except the selector in parentheses.
:eq()	Elements with an index number equal to the parameter.
:gt()	Elements with an index number greater than the parameter.
:lt()	Elements with an index number less than the parameter.
:header	All h1 – h6 HTML tags.
:animated	Any element being animated.
:focus	The element which has focus (an input item such as a field, checkbox, button, or link).
:empty	Elements with no children.
:parent	Elements that have a child node.
:has(selector)	Elements contain atleast one of the elements that match the selector in parentheses.
:contains(‘text’)	Elements that contain the specified text in parentheses.
:hidden	Elements that are hidden.
:visible	Elements that exist and take up space in the layout of the page.
:nth-child(exp)	Elements that match the mathematical pattern. IE –  div :nth-child(2+1)
:first-child	First child from the current selection.
:last-child	Last child from the current selection.
:only-child	The only existing child of the matching element.
[attribute]	Elements that have the specified attribute value – IE – [name^ = “value”]
:input	Elements with input.
:text	Elements with text.
:password	Elements with password inputs.
:radio	Elements with radio buttons.
:checkbox	Elements with checkboxes.
:submit	Elements with submit buttons.
:image	Elements with images.
:reset	Elements with reset buttons.
:button	All buttons.
:file	Elements with file inputs.
:selected	All items from drop-down lists.
:enabled	All enables elements, including defaults.
:disabled	All disables elements.
:checked	All checked checkboxes or radio buttons.

If there’s anything that I’ve missed or more explanation that you’d like to see, feel free to leave a comment.

Help other's to help yourself !!

Export HTML table to Excel file

<!-- https://github.com/linways/table-to-excel -->

<script src="https://cdn.jsdelivr.net/gh/linways/table-to-excel@v1.0.4/dist/tableToExcel.js"></script>

function exportReportToExcel(c) {

  let table = $("#feedbackExport2Excel"); // you can use document.getElementById('tableId') as well by providing id to the table tag

  let fileName = "Feedback";

  TableToExcel.convert(table[0], { // html code may contain multiple tables so here we are refering to 1st table tag

    name: `${fileName}.xlsx`, // fileName you could use any name

    sheet: {

      name: 'Sheet 1' // sheetName

    }

  });

}//exportReportToExcel

Simple way to find Index value from JSON Array

Simple way to find Index value from JSON Array 

var data = [{"name":"placeHolder","section":"right"},{"name":"Overview","section":"left"},{"name":"ByFunction","section":"left"},{"name":"Time","section":"left"},{"name":"allFit","section":"left"},{"name":"allbMatches","section":"left"},{"name":"allOffers","section":"left"},{"name":"allInterests","section":"left"},{"name":"allResponses","section":"left"},{"name":"divChanged","section":"right"}];

var index = data.findIndex(obj => obj.name=="allInterests");

console.log(index);

Add days to a Date using JavaScript

Many times I have face this issue, and hope you too.. this is simple 3 line of code will help and fix this problem.

let days =7 ; // we are going to add 7 days to a date

let cdt = new Date('2021-01-10'); // your date value

let tdt = cdt.setTime(cdt.getTime() + (days * 24 * 60 * 60 * 1000)); // calculation for adding 7 days and adding to time

let targetDT = new Date(tdt).format("yyyy-MM-dd"); // converting back from time to date 

// Output for targetDT will be "2021-01-17"

// With function...

function addDays(theDate, days) {

    return new Date(theDate.getTime() + days*24*60*60*1000);

}

var newDate = addDays(new Date(), 5);

Hope this will help you...

JavaScript to get index from a JSON object with value

 In modern browsers you can use findIndex:

var students = [ {id: 100 }, {id: 200}, {id: 300}, {id: 400}, {id: 500} ]; var index = students.findIndex(std=> std.id === 200);

But this function is not supported by even not so old versions of a few browser as well as in IE (EDGE supports it). So below is a workaround using javascript: You can use either Array.forEach or Array.find or Array.filter

var students = [ {id: 100 }, {id: 200}, {id: 300}, {id: 400}, {id: 500} ]; var index = -1; var needle = 200; var filteredRes = students.find(function(item, i){ if(item.id === needle){ index = i; return i; } }); console.log(index, filteredRes); /*Result: 1 Object { id: 200 }*/

This method takes little more overhead as it loops through the whole object to search for the match. So, for lengthy JSON data, this method is not suggested(even though it gets the work done).