Skip to content

Class10.md

Latest commit

 

History

History
63 lines (42 loc) · 2.47 KB

Class10.md

File metadata and controls

63 lines (42 loc) · 2.47 KB

JavaScript Error Handling And Debugging

order of execution

  • To find the source of an error we need to know the order in which statements are executed some tasks cannot complete until another statement or function has been run

execution contexts

  • Every statement in a script lives in one of three execution contexts

  1. GLOBAL CONTEXT Code that is in the script, but not in a function. There is only one global context in any page.

  2. FUNCTION CONTEXT Code that is being run within a function.

  3. EVAL CONTEXT Text is executed like code in an internal function called eval

Each time a script enters a new execution context there are two phases :

  1. PREPARE
  2. EXECUTE

Error objects : can help to find where are the mistakes and browsers have tools to help you read them

  • When an Error object is created, it will contain the following properties
PROPERTY DESCRIPTION
name Type of execution
message Description
file Number Name of the JavaScript file
line Number Line number of error
  • There are seven types of built-in error objects in JavaScript
PROPERTY DESCRIPTION
Error Generic error - the other errorsare all based upon this error
Syntax Error Syntax has not been followed
ReferenceError Tried to reference a variable that isnot declared/within scope
TypeError An unexpected data type that cannot be coerced
Range Error Numbers not in acceptable range
URI Error encodeURI ().decodeURI(),and similar methods used incorrectly
EvalError eval () function used incorrectly

Deal with Error

  • track down the source of the error and fix it there are developer tools available in browser can help to to track down the error

  • The JavaScript console will help u when there is a problem with a script, where to look for the problem, and what kind of issue it seems to be

  • The JavaScript console is just one of several developer tools that are found in all modern browsers

  • The console will show when there is an error in JavaScript

Summary

  • Debugging is the process of finding errors. It involves a process of deduction

  • The console helps narrow down the area in which the error is located

  • JavaScript has 7 different types of errors Each creates its own error object, which can tell you its line number and gives a description of the error