Error Handling and Debugging

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• What is error handling and debugging? Errors, bugs, and therefore debugging are a part of life for a programmer. … Dealing with errors actually involves two very different processes: error handling and debugging. Error handling is a combination of coding and methodology that allows your program to anticipate user and other errors.

1. The greeting variable gets its value from the greetUser() function.
2. greetUser() creates the message by combining the string ‘He 11 o ‘ with the result of getName ().
3. getName () returns the name to greetUser().
4. greetUser() now knows the name, and combines it with the string. It then returns the message to the statement that called it in step 1.
5. This greeting variable is written to an alert box.

• execution contexts: is defined as the environment in which the JavaScript code is executed. By environment, I mean the value of this , variables, objects, and functions JavaScript code has access to at a particular time.

Variable Scop :scope is function-based while context is object-based. In other words, scope pertains to the variable access of a function when it is invoked and is unique to each invocation. Context is always the value of the this keyword, which is a reference to the object that “owns” the currently executing code.

• Stack

• ERROR OBJECTS

Browser support: Represents a run-time error caused by a script operation. JavaScript interpreters throw an Error object, when a script error (exception) occurs. In some cases when the error is caused by a DOM operation, JavaScript interpreters throw an DOMException object, not an Error object.

• HOW TO DEAL WITH ERRORS

  1. A try-catch-finally statement is a code or program that handles exceptions.
  2. The try clause runs the code that generates exceptions.
  3. The catch clause catches exceptions that are thrown.
  4. A finally clause always gets executed.
  5. The throw statement generates exceptions.
• DEBUGGING TIPS
  1. Outputting JavaScript debugging messages to the browser. ‍One of the easiest ways to debug JavaScript has always been to output data to the browser. …
  2. Popping up messages with alert() …
  3. Logging lines to console with console.log() …
  4. Pausing code execution with the debugger …
• common errors

1. Uncaught TypeError: Cannot read property. … 2. TypeError: ‘undefined’ is not an object (evaluating. … 3. TypeError: null is not an object (evaluating. … 4. (unknown): Script error. … 5. TypeError: Object doesn’t support property. … 6. TypeError: ‘undefined’ is not a function.

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