NOTE: All images from Jonas Schmedtmann's The Complete Javascript Course 2020

Execution Context: Variable Environment

Hoisting and the TDZ

Code Examples

Hoisting Variables

• at the point where we console.log the variables, var is undefined, while let and const are uninitialized (they are in the TDZ)
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• var creates a property on the global window object, while const and let do not
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Hoisting Functions

• only the regular function addDecl can be accessed before it occurs in the code
• here addExpr and addArrow are defined as consts so they are in the TDZ
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• here addExpr and addArrow are defined as vars so they are undefined at the time they are called, so they can't be called or accept arguments
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Be Careful

• numPoducts is undefined, which is a falsy value, so it enters the if statement even though it hasn't been initialized yet
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  • this kind of thing would be a hard big to find in a large codebase
  • best practices for clean code (according to Jonas):
    • try to always use const if possible, then let if you really need to change it later
    • declare all variables at the beginning of their scope
    • declare all functions first and only use them after they are declared (even function declarations)