Don’t catch Your Girlfriends error, catch your programs Error😂— JavaScript

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What is Error?

Every programmer in the world is familiar with the word is “Error”. From beginner to expert, a programmer always has been the victim of this trouble. It is a problem that occurs in the program. Today, I will talk about handling of error that is “try…catch”. Here, try means test a block of codes for checking errors. And catch statement helps to handle the error.

The “try…catch” syntax

There are two blocks in “try…catch”, try and catch.

try {
 // code testing process
} catch (err) {
 // error handling process
}

From the flowchart:

1. Firstly, try statement is executed.
2. If no errors occurred, it simply ignores catch statement but if errors occurred, it ignores try statement and execute catch statement.

An example about this:

try {
alert(‘try runs because the code has no errors’);
} catch (err) {
alert(‘Catch error’); // (3)
}

Do You know try…catch only works for runtime errors?

A program during execution is called runtime errors. The main purpose of try…catch to work, the code must be runnable.

try {
 {{{{{
} catch (err) {
 alert(“Error has occured”);
}

try…catch works synchronously

If a programmer used setTimeOut method, then try catch won’t catch it.

try {
 setTimeout(function() {
 myVariable
 }, 1100);
} catch (err) {
 alert( “didn't work” );
}

But, if you want to catch an exception inside a function try…catch must be used.

setTimeout(function() {
 try {
 myVariable;
 } catch {
 alert( “Error” );
 }
}, 1000);

Error Object

When an error occurs, JavaScript generates an object that are passed as an argument to catch.

try {
 // code
} catch (err) { //error object
 // code
}

“catch” binding

If we don’t need any details information about error, catch may ignore it.

try {
 // code
} catch { // without err
 // code
}

Using “try…catch”

Let’s go to a real life example, JSON. We mainly used to get the decoded data by using JSON parsing. A simple example of JSON is:

json = ‘{“name”:”Mahmudur”, “age”: 23, “occupation”: “Web Developer”}’;

If the json is not correct, it generates an error.

let json = “{ wrong json }”;
try {
 let user = JSON.parse(json); 
 alert( user.age ); // doesn’t work
} catch (err) {
 alert( err.name );
 alert( err.message );
}

Own errors

Sometimes, you see that json is syntactically correct but you don’t have a occupation property. See this.

let json = ‘{ “age”: 23 }’;
try {
 let user = JSON.parse(json); // ← no errors
 alert( user.occupation );
} catch (err) {
 alert( “no execution” );
}

instanceof operator

We can check the type of error by using instanceof operator.

try {
 varA = { /*…*/ };
} catch (err) {
 if (err instanceof ReferenceError) {
 alert(‘Error has occured’);
 }
}

Reference error mainly used for undefined variable.

try…catch…finally

finally statement used to execute the code after try and catch. The code is:

try {
 // code
} catch (err) {
 // code
} finally {
 // code
}

Today, that’s all about this. Thank You. 😉