Error Handling:
Different types of errors during JavaScript code execution.
How to create JavaScript try and catch statements:-
Try & catch:
try {
// code…
} catch (err) {
// error handling
}
The try statement during execution helps to test a block of code for errors.
If an error in the try block, then the catch statement help to execution a block of code:
Example:
try {
alert(“hello Bangladesh”)
alert(Bangladesh is beautiful)
alert(“hello Bangladesh”)
} catch (error) {
alert(‘error massage’,error)
}
2. Block Bindings
Two more new keywords are coming to ES6, let and const.
The first of two new keyword we can say is a let like var But const is a different.
var keyword Example:
var name = ‘rkreza’;
console.log(‘My name is: ‘ + name);
name = ‘rezaul Karim’;
console.log(‘My name is: ‘ + name);
output:
My name is: rkreza
My name is: rezaul karim
Let keyword Example:
let name = ‘rkreza’;
console.log(‘My name is: ‘ + name);
name = ‘rezaul Karim’;
console.log(‘My name is: ‘ + name);
output:
My name is: rkreza
My name is: rezaul karim
Const:
Const means constant, whose value cannot be changed. You declare something with const you can’t change it after that.
Example:
const name = ‘rkreza’;
console.log(‘My name is: ‘ + name);
output:
My name is: rkreza
3.Funtion
A JavaScript function is a set of code that is created to perform a specific task.
To create a JavaScript function, the first write function keyword, then the name of function and right side () and the right side Curly brace {}.
Example:
function display() {
console.log(“Hello Bangladesh!”);
}
display();
output: Hello Bangladesh
4. Spread Operator
The spread operator basically spreads the array and the object.
Example:
We have an array of number
Let number = [22,33,44,55,66,77,88];
Spread operator apply
Let newNumber = […number,45,25,35,65,75,85];
5. Types of Values
JavaScript Supports six types of Data Types.
I.Boolean
II.Number
III.String
IV.Null
V.Undefined
VI.Symbol
I.Boolean
This data type only two types of value, true and false
Example:
Boolean (1)
True
Boolean(null);
False
II.Number
When a Data represents only Number, those Data is called Number Data Type in JavaScript.
data types: numbers, strings, objects and more:
Example:
let number = 16; // Number
let lastName = “rezaul”; // String
let name = {firstName:”rezaul”, lastName:”karim”}; // Object
III.String
When a Data represents only String, that is, a series of certain characters.
Example:
let lastName = “rezaul”; // String
V.Undefined
when a variable is declared but nothing is assigned or initialized. The only value of this data type is undefined.
Example:
function test(data) {
if (data === undefined) {
return ‘Undefined value!’;
}
return data;
}
let x;
console.log(test(x));
VI.Symbol
This gives each data a unique key
Example:
document.write(Symbol(‘dummy’) === Symbol(‘dummy’));
document.write(“<br>”);
document.write(‘dummy’===’dummy’);
6. Block-Level Functions:
A block statement is used to group zero or more statements.
Example:
alert(function(){
‘use strict’;
function f() { return 1; }
{
function f() { return 2; }
}
return f() === 1;
}());
6. Arrow Functions
If the function has only one statement, and the statement returns a value:
Example:
let display = () => {
return “Hello World!”;
}
7.anonymous function
Aanonymous function is a function without a name.
Example:
(function () {
console.log(‘Bangladesh’);
})
8. join
Connects all elements of an array to a string.
Example:
var laptop = [“dell”, “lenovo”, “Apple”, “Hp”];
laptop.join();
console.log(laptop)
9.pop():
JavaScript uses the pop () method to remove or delete a value from the end of an array.
Example:
var laptop = [“dell”, “lenovo”, “Apple”, “Hp”];
laptop.pop();
10. shift ()
JavaScript uses the shift () method to remove a value from the start array.
Example:
var laptop = [“dell”, “lenovo”, “Apple”, “Hp”];
laptop.shift();
console.log(laptop)