Read: 10 - JS Debugging

From the Duckett JS book:

JavaScript book, Ch. 10, Error Handling & Debugging

• the javascript interpreter processes one line of code at a time. So, When a statement needs data from another functionm it stacks(or piles) the new function on top of the current task.

• Each time a new item is added to the stack, it creates a new execution context.

  Execution context & Hoisting

• Each time a script enters a new execution context, there are two phases of activity:
  1. Prepare -> when creates The new scope/Variables, functions, and arguments/ or determines The value of the this keyword.
  2. Exexcute -> when assign values to variables/Reference functions and run their code/Execute statements.

• For hoisting: • Call functions before they have been declared/Assign a value to a variable that has not yet been declared .

• Functions in JavaScript are said to have lexical scope -> the scope is the current execution context’s variables object, plus the variables object for each parent execution context.

• If a JavaScript statement generates an error, then it throws an exception. At that point, the interpreter stops and looks for exception-handling code.

• Error objects can help you find where your mistakes are and browsers have tools to help you read them.

• JavaScript has 7 different types of errors:
  1. Syntax Error.
  2. ReferenceError -> When the variable is not declared or is out of scope.
  3. EvalError -> Incorrect use of eval() function.
  4. URI Error -> Incorrect use of URI functions.
  5. Type Error -> Value is unexpected data type.
  6. RangeError -> Number outside of range.
  7. Error(The generic Error object) ->Is the template (or prototype) from which all other error objects are created.

• NaN (Not An Error)-> Indicates that a value is not a legal number,(JavaScript considers the type of NaN to be number).

  How to deal with errors ?

  1. Debug the script to fix errors -> track down the source of the error and fix it.

  2. Handle errors gracefully-> using try, catch, throw, and finally statements(gives user helpful feedbacks).

• understand execution contexts and stacks, helps you to find the error in your code.
• Debugging (involves process of deduction): helps you eliminating potential causes of an error.
• We can use console to look at errors.