Basic JavaScript Concept(string, number, array)

##Sring

In JavaScript, the textual data is stored in a string that is wrapped by a single quote(‘) or double quote(“).

let singleQuote = ‘single quote’;

let doubleQuote = “double quote”;

#String indexOf()

The string object’s indexOf() method returns a number value that gives the index number of the first letter of that word. Index number starts from 0.

Example:

let example = ‘Bangladesh is a very beautiful country. There are 64 districts in our country.’

let findIndex = ‘very“;

console.log(example.indexOf(findIndex));

// It will return value16 . Index number count starts from the letter “B”. White space is also counted in index number.;

// If that word not exist in the sentence it will return -1;

#String chartAt()

The string object’s charAt() method returns the letter of the index number position. Or use a squire bracket way to get the character at the position.

Example:

let str = “Hello World”;

console.log(str[3]); // answer will be “L”.

Or conole.log(str.charAt(3)); // “L”

Most commonly used squire bracket([]) way. That is the modern way. While charAt() exists mostly for historical reasons.

There is one difference between the two of them. If no character is found, [] returns undefined, and charAt returns an empty string:

Example:

let str = “Hello World”;

console.log(str[100]); // undefine

conole.log(str.charAt(100)); // empty string “ “

#String slice()

The string object’s slice() creates a new string from the old string part without modifying the original string.

str.slice(where form start, where to end) // basic structure .

It returns the part of the string from start to (but not including) end.

Example:

let str = “Hello World”

str.slice(0, 7); // “Hello Wo”

If there is no second argument, then slice() goes till the end of the string:

Example:

str.slice(2); // “llo World”

Negative values for start/end are also possible. They mean the position is counted from the string end:

Example:

str.slice(-3, -1) // “rl”

// start at the 3rd position from the right, end at the 1st from the right

##Number

#Math.abs()

The number object abs() method always returns an absolute value of the number. If the number is negative it will convert it into a positive number.

Example:

let number = -10;

console.log(Math.abs(number)) // 10.

If the number is positive it will return a positive value of the number.

#Math.Floor()

The number object floor() method always returns the largest integer less than or equal to a given number. That’s mean if number is 1.9, it will return 1, event if number is 1.01, it will also return 1,

Example:

let number = 1.2;

console.log(Math.floor(number)); // 1;

let number2 = 1.99

console.log(Math.floor(number2)); // 1

#Math.ceil()

The number object ceil() method always returns the integer number greater than or equal to a given number. That’s mean if number is 2.9, it will return 3, event if number is 2.01, it will also return 3,

Example:

let number = 3.2;

console.log(Math.ceil(number)); // 4;

let number2 = 3.99

console.log(Math.ceil(number2)); // 4

###Array

It’s a collection of data where stores multiple data like strings, numbers, objects. Separated by comma and wrapped by squire bracket [].

#find()

The find() method returns the value of the first element in an array that passes a test. If it finds an array element where the function returns a true value, find() returns the value of that array element and does not check the remaining values. Otherwise, it returns undefined

Example:

const array1 = [5, 12,17, 2, 10, 8, 13, 44 ];

const found = array1.find(element => element > 10);

console.log(found); // return 12;

#filter()

The filter() method calls a call-back function once for each of the array elements and creates a new array with all the values which the call-back function returns true. It means it constructs a new array with all elements that the call-back function’s condition returns true.

Example:

const array = [5, 12,17, 2, 10, 8, 13, 44 ];

const filterData = array.filter(element => element > 10);

console.log(found); // return[12, 17, 13, 44];

#push()

The push() method is a way to add new elements in an array. It adds an element to the end of the array and returns a new length. You can push multiple elements at a time.

Example:

const oldArray = [12, 1, 23, 54, 2, 22, 29];

const newArray = oldArray.push(5);

// return [12, 1, 23, 54, 2, 22, 29, 5]

#shift()

The shift() method removes the first element from the array and returns a new length. It creates a new length of the array.

Example:

const oldArray = [12, 1, 23, 54, 2, 22, 29];

console.log(oldArray.shift()); // 12

console.log(oldArray) // return [ 1, 23, 54, 2, 22, 29 ]