JavaScript error messages && debugging

• as a developer most of the time i will spend time dealing with errors.
• and in order to handle errors am should use errors messages from console of browser or terminal where I like to read it or not.

types of errors i will be dealing with:

syntax error :

• when i run javascript code, the v8 engine parse the code and check for syntax errors before they construct an abstract syntax tree.
• when syntax error found, there will be message in console say error type : syntax error.
• e.g. JSON.parse({‘key’:’value’}) ===> message syntax error similar to this Uncaught SyntaxError: Unexpected token o in JSON at position 1.

reference error :

• when i try to use a variable not defined i receive this error.
• it means i am trying to use variable that is not refering to a value inside the memory.
• it also happen when i try to use a variable before it’s declaration like let and const.
• to solve it declare it before using it.

range error:

• it happen when i try to access index in array like -1, because array start from 0.
• for example

   let arr = []
   console.log(arr.length -1)
  

  Type errors

• type errors happen when i try to perform incompatable code with the variable type.
• for example run number method or array method on variable hold undefined value.
• to solve this just make sure to declare the variable correctly.

Debugging in JavaScript:

• one way to console.log variable or the expected error i want to check.
• other way is to use breakpoint can be achieved by putting a debugger statement in your code in the line you want to break.
• this is handy when i want to debug huge cycles for specific values.
• example the breakpoint will point stop when the index reaches 40.
• I can do it in Node.js as well by open debug tab and configure it like this.
• I can run the debugger by pressing F5.

Call stack

• the call stack is the way my program has been implemented until the point where i will get error.