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Understanding the JavaScript Call Stack
JavaScript Error Messages

Understanding the JavaScript Call Stack

1. What is a ‘call’?
   • Function invocation
2. How many ‘calls’ can happen at once?
   • In V8, the number of recursive calls you can make depends on two quantities: the size of the stack and the size of the stack frame (holding parameters and local variables).
3. What does LIFO mean?
   • Last in First Out
   • 

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

   function firstFunction(){
      console.log("Hello from firstFunction");
   }
   
   function secondFunction(){
      firstFunction();
      console.log("The end from secondFunction");
   }
   
   secondFunction();
   

5. What causes a Stack Overflow?
   • A stack overflow occurs when there is a recursive function (a function that calls itself) without an exit point. The browser (hosting environment) has a maximum stack call that it can accomodate before throwing a stack error.

JavaScript Error Messages

1. What is a ‘reference error’?
   • This is as simple as when you try to use a variable that is not yet declared you get this type os errors. console.log(foo) // Uncaught ReferenceError: foo is not defined
2. What is a ‘syntax error’?
   • This occurs when you have something that cannot be parsed in terms of syntax, like when you try to parse an invalid object using JSON.parse.
   • JSON.parse( {'foo': 'bar'} ) // Uncaught SyntaxError: Unexpected token o in JSON at position 1
3. What is a ‘range error’?
   • Try to manipulate an object with some kind of length and give it an invalid length and this kind of errors will show up.

   var foo= []
   foo.length = foo.length -1 // Uncaught RangeError: Invalid array length
   

4. What is a ‘tyep error’?
   • this types of errors show up when the types (number, string and so on) you are trying to use or access are incompatible, like accessing a property in an undefined type of variable.

   var foo = {}
   foo.bar // undefined
   foo.bar.baz // Uncaught TypeError: Cannot read property 'baz' of undefined
   

5. What is a breakpoint?
   • A break point is a point set in your code to have it pause execution which you can then step through one line at a time.
6. What does the word ‘debugger’ do in your code?
   • The breakpoint can also be achieved by putting a debugger statement in your code in the line you want to break.

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