Basics of JavaScript

JavaScript is a programming language to create dynamic web sites. JS supports Object oriented programming and functional programming. It is a dynamic typed language, which means we don’t need to declare type of variables. Js variables can be of different types. Such as:

· Numbers

· Strings

· Objects

· Arrays

· Functions

· Boolean

Numbers:

If variable presents in numbers than it called Numbers variable. String or other can be converted to number if value given in Number(value) function.

Number(‘abc’) // output will be Nan

Number(‘456’) // output will be 456

Some properties of Numbers are:

· Number.Max_Value(returns maximum numeric value)

· Number.Min_Value(returns minimum numeric positive value)

· Number.NaN(returns Not a Number)

Some popular methods of numbers are:

· Number.isInteger(5) [check 5 is integer or not]

· Number.parseFloat(‘1.25jhfg’) [parses the argument and return 1.25]

· Number.parseInt(‘1.25jhfg’) [parses the argument and return 1, only integer value, no floating value]

· Number.parseFloat(‘1.35478’).toFixed(1) [parses the argument and return 1.3 , 1 position value after .]

· Number. parseFloat(‘1.35478’).toPrecision(4) [parses the argument and return 1.354, as per precision value ]

Strings:

If variable represents in one or more letters within the quotation, it called strings.

Property of strings:

const check = ‘dgtre sgdju jkuyt’;

console.log(check.length); output will be 15

Some popular methods of strings are:

· charAt(value) method return that alphabet of a string as specified position as value.

const str=”njhtd”;

console.log(str.charAt(2)); // output will be h

· concat() method joins strings to give a new string.

const str1 = ‘Tashfia’;

const str2 = ‘Hoque’;

console.log(str1.concat(str2)); // output: “TashfiaHoque”

console.log(str1.concat(‘ ‘, str2)); // output: “Tashfia Hoque”

· indexOf() method returns the first matched index of a character, if not returns -1.

const p =”cat sat on a mat and rat sat on a cat”;

const find = ‘cat’;

console.log(p.indexOf(find)); // output: 0

· includes() method returns the search item exists or not exist in a string.

const p =”cat sat on a mat and rat sat on a cat”;

const find = ’and’;

console.log(p.includes(find)); // output: true

· lastIndexOf() method returns the last index value if search item has mulitiple position.

const p =’cat sat on a mat and rat sat on a cat’;

const find = ‘cat’;

console.log(p.lastIndexOf(find)); // output: 34

· replace() method returns a new string by replacing old one with matches of a pattern. If pattern is regular expression then it will return only the first matched.

const p =’cat sat on a mat’;

const find = ‘cat’;

console.log(p.replace(find, ‘rat’)); //output: rat sat on a mat