Jon Rumsey

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Memory Usage Notes and References

Understanding the JS Call Stack

• The Call Stack is for function invokation.
• There is only one Call Stack.
• Functions are executed one at a time and removed once completed successfully.
• The Call Stack is a LIFO (Last In First Out) data structure.

JS Q and A

What is a ‘call’?

An invokation of a function.

How many ‘calls’ can happen at once?

One.

What does LIFO mean?

It is a stack (or array) where the last item in is always the first item out.

Draw an example of a call stack and the functions that would need to be invoked to generate that call stack.

[A| | | | ]
 ^
 PUSH fx(a)

[A|B| | | ]
   ^
   PUSH fx(b)

[A|B|C| | ]
     ^
     PUSH fx(c)

     POP => function(c)
     v
[A|B| | | ]

[A|B|D| | ]
     ^
     PUSH fx(d)

     POP => function(d)
     v
[A|B| | | ]

   POP => function(b)
   v
[A|B| | | ]

Etcetera.

What causes a Stack Overflow?

Googling the answers to tough coding questions.
A recursive function that calls itself without an exit condition.
More functions are placed on the stack than there is memory allocated to store them.

JS Error Messages and Debugging

Tools

• The debugger; statement: Stops RunTime execution of the code at that code line.
• The console.trace(); statement: Outputs the stack trace (labels) to the Console.
• Insert a 'try-catch' block into areas of code that might fail, overflow, or where error flow control is needed.
• RunTime Errors (which is all of them in javascript) are only detectable at RunTime.
• Quokka and ESLint: Evaluate code as you type; Display warnings and error messages about code style and syntax during developing time.

Error Messages and Debugging Q and A

What is a ‘reference error’?

Attempting to use an uninitialized variable.

What is a ‘syntax error’?

Incorrect syntax was used when defining an expression.

What is a ‘range error’?

When indexing into an iterable, selecting an index ID that is not included in the iterable.

What is a ‘tyep error’?

Not sure about "tyep error" but a Type Error happens when tyring to use incompatible types together, such as an Array and a Number.

What is a breakpoint?

A developer-assigned location in the code where the RunTime will halt when reached so that value and reference types can be examined.

What does the word ‘debugger’ do in your code?

It stops code execution at the line where the keyword is.

Resources

Understanding the JS Call Stack on Free Code Camp.org
JS Error Messages and Debugging codeburst.io
MDN on javascript Errors
List of Udemy courses for full-stack developers at CodeBurst.io
Brandon Morelli on Medium.com

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