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CLASS-10

JAVASCRIPT

ERROR HANDLING & DEBUGGING

JavaScript can be hard to learn and we all make mistakes. In order to find and correct errors is important to understand the Execution Contexts and Variable Scope.

  • Global Context: Refers to code that in the script but not in a function.
  • Function Context: Refers to code that is being run within a function.
  • Global Scope: When a variable is declared outside a function.
  • Function-Level Scope: When a variable is declared within a function.

The Execution Context has two phases:

  1. Prepare: Here the new scope is created. Variables, functions and arguments.
  2. Execute: Here is when it assigns values to variables, references functions, run their code and execute statements.
  • The Stack: JavaScript processes one line of code a the time. When a statement needs data from another function, it stacks the new function on top of the current task.

TYPES OF ERRORS

  1. SyntaxError: Incorrect use of rules of the language.
  2. ReferenceError: Variable that is not declared or is out of scope.
  3. URIError: When / ? & # : ; are not escaped in URIs.
  4. TypeError: When trying to use an object or method that does not exist.
  5. Error: Generic template from which all other errors are created.
  6. RangeError: When we call a function using numbers outside of its accepted range.
  7. NaN: When performing a math operation using a value that is not a number.

  • Debugging: It is the process of finding errors. A process of deduction to figure out what the problem is, where is it, the cause of it and how to fix it. We can use Dev Tools & JavaScript Console to do this.

  • try, catch, finally: We can use these statements in advance if we know we may get an error.

Things I want to know more about

  • Dev Tools and JavaScript Console.

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