Execution Context

Question 1

JavaScript code is evaluated as 1 of the following 3 environments.

Answer 1

1. ) Global code
2. ) Function code
3. ) Eval code

Question 2

When running a function in JavaScript we create a new …

Answer 2

Execution Context

Question 3

Is there a limit to function execution contexts?

Answer 3

Technically no, depending on the host machine’s resources.

Question 4

How many global execution contexts can there be?

Answer 4

Only ever one.

Question 5

A new execution context creates a new …

Answer 5

Scope

Question 6

The JavaScript interpreter in a browser is implemented as a … thread

Answer 6

single

Question 7

How many things can happen at a time in a single-threaded environment?

Answer 7

One

Question 8

What type of data structure is the Execution (call) Stack?

Answer 8

A LIFO (last in - first out) data structure

Question 9

When a browser first loads a script, we enter the … context

Answer 9

Global execution context

Question 10

What happens when a context has finished executing?

Answer 10

The context is popped off the stack and control returns to the context below it until the global context is reached again.

Question 11

Name at least 3 key points about the execution stack.

Answer 11

1. ) The execution stack is single-threaded
2. ) The execution stack follows synchronous execution
3. ) There is only ever 1 global context
4. ) There are technically infinite function contexts
5. ) Each function call creates a new execution context

Question 12

There are 2 phases / stages to every call to an execution context. They are?

Answer 12

1. ) Creation Stage

2. ) Activation / Code Execution Stage

Question 13

What happens in the Creation Stage of a call to a new execution context?

Answer 13

1. ) It creates a scope chain
2. ) It creates an activation object (variables, functions, objects)
3. ) It determines the value of ‘this’

Question 14

What happens in the Activation Stage of a call to a new execution context?

Answer 14

Assign values, references to functions and interpret / execute code.

Question 15

If an execution context was to be represented visually as an object, what would it look like?

Answer 15

It would have a scopeChain property, a variableObject property and a this property.

Each of these properties would have a value of an object.

Question 16

When is the executionContentObject created?

Answer 16

When the function is invoked, but before the function has been executed.

Question 17

In what stage is the executionContextObject created?

Answer 17

in the Creation Stage

Question 18

Why can we access a function before we have declared it in the code (e.g. top to bottom)

Answer 18

Because in the Creation Stage the executionContextObject has been created and a variableObject contains a pointer to the function in memory

Question 19

Why is a variable undefined but does not call an error when referred to?

Answer 19

Because the variableObject contains an identifier for the variable with the value of undefined, even if a value is not assigned until the Execution Stage

Question 20

In the Creation Stage, in which order are function and variable identifiers installed?

Answer 20

1. ) Function

2. ) Variable

Question 21

If a property name exists on the variableObject, what happens when it is declared a second time?

Answer 21

We skip the subsequent declaration.