1 . Discuss about Error handling
- in error handling using Four keyword
- try
- catch
- finally
- throw
2. why use error handling?
Then if we create large apps suppose 1000 line code in the run time has found anyone line error we can not see our output for that reason using error handling. if we use try catch it’s ignore the error code and display the output.
declaration of try..catch
try{
code….
}
catch(){
}
catch is a function it work is before find execution error handle
try work where error have a possibility that’s place
Example:
try{
alert(“Hello everyone”);
alert(“Bye Bye”);
}
catch(){
alert(“Inside catch block”)
}
if try block code is ok catch block does not work but in try block have identify error then catch is work and ignore the error and the output
3. try..catch only work for run time error
JavaScript engine first read the code and then run
2. try catch use finally block
finally block always work if error have or no error it give the output
try{
alert(“Hello everyone”);
alert(“Bye Bye”);
}
catch(err){
alert(“Inside catch block”)
}
finally{
alert(“God bless you”);
}
1. throw statement
throw statement create custom error.
The throw operator generates an error.
throw <error object>
- There may be no catch section or no finally, so shorter constructor and try..catch are also valid.
3 .Coding Style
Our code must be as clean and easy to read as possible.
coding style is the actually the art of programming
- Curly Braces
- line lentgh
- Indents :
- semicolon
- nesting lavel
- function placement
- style guide
- automated linters
this is very important for the coding style
4 .JavaScript comments
well programmer maintain all code decoration comment is one of them
// this is single-line comment
/*…….*/ multiline comment
those use the visual studio code or VSCode use
ctrl +slash
5. ES6/ECMAScript
block statement or compound statement in block statement code execute only inside block not other
example :
var x = 1;
let y = 1;
if (true) {
var x = 2;
let y = 2;
}
console.log(x);
expected output: 2
console.log(y);
expected output: 1
6.Hoisting
hoisting is like scope where we declare variable it’s define and when we declare variable how javaScript deal that variable that is hoisting
- Hoisting Bangla meaning Uttolon or Uporer dike tola
7. Block-level declaration, Block-Binding
Block-level declarations are those that declare variables that are inaccessible outside of a given block scope. Block scopes are created:
- Inside of a function
- Inside of a block (indicated by the
{
and}
characters)
var/let/const
var
- it al time can use
2. var is a function scope inside the function area it can call
example:
if(true){
var myVariable=“This is var”;
}
console.log(myVariable);
let
- if have possibility to change the variable name then use the let l
example :
let patient=20;
patient=40;
if(true){
let letVariable=“this is let”;
console.log(letVariable);
}
2. let is block scope it only work in block area not other
const
1 .if variable value do not have to chance to change in next that time use the
const.
2. const fix no change
example:
const country=“Bangladesh”;
console.log(country);
8 .Function default parameter
when call the function if do not given parameter but we want to run the code that’s why use default parameter
example:
9 .Spread Operator
spread operator (…)
- The spread operator allows an expression to be expanded in places where multiple arguments (for function calls) or multiple elements (for array literals) are expected.
2. using spread operator do concatenate work easily
example:
10. Arrow function
An arrow function expression is a compact alternative to a traditional function expression but is limited and can’t be used in all situations.
in arrow function minimum if there are two parameter use ()
*Multiline arrow function