No matter how great we are at programming, sometimes our code has errors. They may occur because of our mistakes, an unexpected user input, an erroneous server response, and for a thousand other reasons.

Javascript has try and catch to handle these errors and respond to users.

try {
    let name = getName();
} catch (error) {
    /*
    * error object that contains at least the name of the error and message that explains the error in detail.
    * Different web browsers may add more property to the error object. 
    * For example, Firefox adds filename, lineNumber, and stack properties to the error object.
    */
    console.log(error);//ReferenceError: getName is not defined
    console.log(error.name + ":" + error.message);//ReferenceError:getName is not defined
}finally {
    console.log("finally");
}

Try and Catch only works synchronously and does not work asynchronously.

/*
* try..catch only works synchronously. It does not work asynchronously.
*/

try {
    setTimeout(function() {
        getName(); // script will die here
    }, 1000);
} catch (error) {
    console.log("Error not caught here.");
}

setTimeout(function() {
    try {
        getName();
    } catch (error) {
        console.log(error);//ReferenceError: getName is not defined
        console.log(error.name + ":" + error.message);//ReferenceError:getName is not defined
    }
}, 1000);

Throw an Error

Use throw new typeOfError to throw an error.

function throwError(){
    throw new Error("Something went wrong due to Error!");
}

function throwReferenceError(){
    throw new ReferenceError("Something went wrong due to ReferenceError!");
}

try {
    throwError();
} catch (error) {
    console.log(error.name + ":" + error.message);
}

try {
    throwReferenceError();
} catch (error) {
    console.log(error.name + ":" + error.message);
}

Types of Error

• Error
• EvalError – an error has occurred in the eval() function. Note: Newer versions of JavaScript does not throw any EvalError. Use SyntaxError instead.
• RangeError – a number “out of range” has occurred
• ReferenceError – an illegal reference has occurred
• SystaxError – a syntax error has occurred
• TypeError – a type error has occurred
• URIError – an error in encodeURI() has occurred

Custom Error

You can create a custom error by extending the Error class

class ValidationError extends Error {
    constructor(message) {
        super(message); // (1)
        this.name = "ValidationError"; // (2)
    }
}

function testValidationError() {
    throw new ValidationError("Whoops!");
}

try {
    testValidationError();
} catch(error) {
    console.log(error.name + ":" + error.message);
    console.log("error stack");
    console.log(error.stack);
}

Source code on Github