Throwing errors in JavaScript

September 10, 2019

Throwing stops execution
Put the throw inside a try .. catch block
Once execution stops, the control will be passed to the first catch block it finds. If no catch then the program will terminate
You can re-throw errors
You can throw different types of errors

code

// throw Examples
throw "Error2"; // generates an exception with a string value
throw 42; // generates an exception with the value 42
throw true; // generates an exception with the value true
throw new Error("Required"); // generates an error object with the message of Required

code

// Errors and Exceptions
console.log(e); // ReferenceError: blah is not defined
console.log(e.stack); // tells you line number, not supported by some
console.log(e.name); // ReferenceError
console.log(e.message); // blah is not defined

Example

code

/*
 * Complete the isPositive function.
 * If 'a' is positive, return "YES".
 * If 'a' is 0, throw an Error with the message "Zero Error"
 * If 'a' is negative, throw an Error with the message "Negative Error"
 */
function isPositive(a) {
  // if (a === 0) { throw 'Zero Error'}
  // if (a < 0) { throw 'Negative Error'}
  // return 'YES'

  if (a >= 1) {
    return "YES";
  } else if (a === 0) {
    // put throw inside a try/catch so the execution doesn't stop
    try {
      throw new Error("Zero Error");
    } catch (e) {
      // e will be whatever error/exception we throwed earlier
      return e.message; // 'Zero Error'
    }
  } else {
    try {
      throw new Error("Negative Error");
    } catch (error) {
      return error.message;
    }
  }
}

Throwing errors in JavaScript

Example

Links