reading-notes-201d25

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Read10

JS Error Handling & Debugging

Debugging is the process of testing, finding, and reducing bugs (errors) in computer programs. The first known computer bug was a real bug (an insect) stuck in the electronics.

• Programming code might contain syntax errors, or logical errors. Searching for (and fixing) errors in programming code is called code debugging.
• If we understand execution contexts (which have two stages) and stacks, you are more likely to find the error in your code.
• 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, so you can try to find the exact error. 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.
  1. RangeError This is thrown when a number is outside an allowable range of values.
  2. ReferenceError
• This error is thrown when a reference made to a variable/item is broken. That is the variable/item doesn’t exist.
  1. SyntaxError
• This is the most common error we encounter. This error occurs when we type code that the JS engine can understand.
  1. TypeError
• TypeError is used to indicate an unsuccessful operation when none of the other NativeError objects are an appropriate indication of the failure cause. TypeError occurs when an operation is performed on a wrong data type. Maybe a boolean is expected but a sting is found.
  1. URIError
• This indicates that one of the global URI handling functions was used in a way that is incompatible with its definition. URI (Uniform Resource Indicator) in JS has the functions: decodeURI, decodeURIComponent, etc. If we call any of them with the wrong parameter we will get a URIError
  1. EvalError This is used to identify errors when using the global eval() function. -This exception is not currently used within this specification. This object remains for compatibility with previous editions of this specification.
  2. InternalError
• This error occurs internally in the JS engine, especially when it has too much data to handle and the stack grows way over its critical limit.
• This occurs when the JS engine is overwhelmed by too many recursions, too many switch cases, etc. If you know that you may get an error, you can handle it gracefully using the try, catch, finally statements. Use them to give your users helpful feedback.