🔰execution context
state to track the execution progress of code.
JS ⟩ concept ⟩ execution context
An execution context contains whatever implementation specific state is necessary to track the execution progress of its associated code.
It may contain (but not limited to) the following：
lexical environment - stores variables/this ...
code evaluation state - state needed to perform/suspend/resume evaluation of the code associated with this execution context.
📘 JS spec ⟩ 8.2 Execution Contexts
At any point in time, there is at most one execution context that is actually executing code. This is known as the running execution context.
A stack is used to track execution contexts. The running execution context is always the top element of this stack.
call stack - track execution contexts.
lexical environment - part of execution context.
lexical environment is part of execution context.
function declaration instantiation - the proccess before calling a function.
scope of a code block - can reach all its parents lexical environment.
this is a property of execution context (more specifically, lexical environment).
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