Different ways to handle JavaScript errors

When executing javascript code, different errors can occur. Errors can be coding errors made by the programmer, error due to wrong input, and other unforeseeable things

try and cath

The try statement allows you to define a block of code to be tested for errors while it is being executed.

The catch statement allows you to define a block of code to be executed if an error occurs in the try block

Example

<p id = "demo"></p>
<script>
try {
addAlert("hellow guest!");
}
catch(err){
document.getElementById("demo").innerHTML = err.message;
}
</script>

EvalError

The EvalError object indicates an error regarding the global eval() function. This exception is not thrown by JavaScript anymore, however, the EvalError object remains for compatibility.

EvalError()

Example

try {
  throw new EvalError('Hello', 'someFile.js', 10);
} catch (e) {
  console.log(e instanceof EvalError); 
  console.log(e.message);              
  console.log(e.name);              
  console.log(e.fileName);            
  console.log(e.lineNumber);          
  console.log(e.columnNumber);      
  console.log(e.stack);
}

InternalError

The InternalError indicates an error that occurred internally in the JavaScript engine.

InternalError()

Example

function loop(x) {
  if (x >= 10) // "x >= 10" is the exit condition
    return;
  // do stuff
  loop(x + 1); // the recursive call
}
loop(0);

RangeError

A Range is thrown if you use a number that is outside the range of legal values.

Example

var num = 1;
try {
num.toPercision(500);
}
catch(err){
document.getElementById("demo").innerHTML = err.name;
}

Type Error

A TypeError is thrown if you use a value that is outside the range of expected types:

Example

var num = 1;
try {
num.toUpperCase();
}
catch(err){
document.getElementById("demo").innerHTML = err.name;
}

URI(Uniform Resource Identifier) Error

A URIError is thrown if you use illegal characters in a URI function:

Example

try {
decodeURI("%%%");
}
catch(err){
document.getElementById("demo").innerHTML = err.name;
}

SyntaxError

The SyntaxError object represents an error when trying to interpret syntactically invalid code. It is thrown when the JavaScript engine encounters tokens or token order that does not conform to the syntax of the language when parsing code.

SyntaxError()

Example

try {
  eval('hoo bar');
} catch (e) {
  console.error(e instanceof SyntaxError);
  console.error(e.message);
  console.error(e.name);
  console.error(e.fileName);
  console.error(e.lineNumber);
  console.error(e.columnNumber);
  console.error(e.stack);
}

ReferenceError

The ReferenceError object represents an error when a non-existent variable is referenced.

ReferenceError()

Example

try {
  let a = undefinedVariable
} catch (e) {
  console.log(e instanceof ReferenceError)
  console.log(e.message)                    
  console.log(e.name)                   
  console.log(e.fileName)                 
  console.log(e.lineNumber)                 
  console.log(e.columnNumber)
  console.log(e.stack)
}

switch statement

the program executes the associated statement.

Example

switch (expression) {
  case label_1:
    statements_1
    [break;]
  case label_2:
    statements_2
    [break;]
    …
  default:
    statements_def
    [break;]
}

Utilizing Error objects

type of error, you may be able to use the name and message properties to get a more refined message

Example

function doSomethingErrorProne() {
  if (ourCodeMakesAMistake()) {
    throw (new Error('The message'));
  } else {
    doSomethingToGetAJavascriptError();
  }
}
⋮
try {
  doSomethingErrorProne();
} catch (e) {               // NOW, we actually use `console.error()`
  console.error(e.name);    // logs 'Error'
  console.error(e.message); // logs 'The message', or a JavaScript error message
}