reading-notes

These are my reading notes for Code Fellows

---

Project maintained by taegorov Hosted on GitHub Pages — Theme by mattgraham

Link Home:

Home

Reading Notes Code 201: Day 10

Notes - JavaScript Book, Ch. 10, “Error Handling & Debugging”

Order of Execution

“the order in which statements are processed”

-Jon Duckett, JavaScript & JQuery, page 452

Execution Context

• Global
• Function
• Eval

Variable Scope

• Global
• Function-Level

2 phases after a script goes into a “new execution context”:

1. Prepare
2. Execute

Preparing creates a new scope, along with functions/arguments/variables. Executing assigns values to those things, references functions, and executes.

Hoisting brings functions/variables to the top of the execution context

Although it seems counter-intuitive, the code below would work just fine:

let userName = newUser ();
function newUser();{
}

That’s because it is handled like this:

function newUser(){
}
let userName = newUser();

This block of similar code would fail, since newUser is inside createGreeting:

let userName = newUser();
function createGreeting(){
    function newUser();
}
}

Functions have lexical scope. “They are linked to the object they were defined within. So, for each execution context, the scope is the current execution context’s variables object, plus the variables object for each parent execution context” (Duckett, JavaScript & JQuery, page 457)

Look for exceptions when trying to find an error in your code

---

Error Objects

Here are some error objects that you might come across in your console:

Property	Description
name	The type of error
message	Description of the error
fileNumber	Name of the JS file
lineNumber	Line number of the error

(note: the above is borrowed heavily from Jon Duckett’s JavaScript & JQuery page 459)

7 Types of Error Objects:

1. Error (generic)
2. SyntaxError
3. ReferenceError
4. TypeError
5. RangeError
6. URIError
7. EvalError

Try, catch, throw, finally statements

Identifying where the problem is:

• Check error messages, they’ll tell you where the error is occurring (line number), along with the cause
• See how far along your code the script is actually running
• Breakpoints
• (Personal addition) - add console.log()

(The book actually mentions console logs later on)

console.group() can group a set of related data

---

Breakpoints

These are what Chance walked you through during Salmon Cookies (when you were working on adding form info to a table)! They allow you to stop a script at any line.

Go into the console > debugger > click on a line

You can also step through the code on the right side of the debugger (also did this with Chance).

Add breakpoints directly to your code with debugger;