Variable declaration using const in Javascript - Step-by-Step Execution

Concept Flow - Variable declaration using const

Start

↓

Declare const variable

↓

Assign initial value

↓

Use variable

↓

Try to reassign?

Yes→Error: Cannot reassign const

No↓

End

This flow shows declaring a constant variable, assigning it once, using it, and that reassignment causes an error.

Execution Sample

Javascript

const pi = 3.14;
console.log(pi);
pi = 3.14159; // Error

Declare a constant pi, print it, then try to change it which causes an error.

Execution Table

Step	Action	Variable	Value	Result/Output
1	Declare const pi	pi	3.14	No output
2	Print pi	pi	3.14	3.14
3	Try to reassign pi	pi	3.14	Error: Assignment to constant variable.

💡 Execution stops at step 3 due to error on reassignment of const variable.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3
pi	undefined	3.14	3.14	3.14 (unchanged, error on reassignment)

Key Moments - 2 Insights

Why can't we change the value of a const variable after declaring it?

Because const variables are read-only after assignment. The execution_table step 3 shows an error when trying to reassign pi.

Does declaring a const variable require an initial value?

Yes, const must be assigned a value when declared. Step 1 shows pi assigned 3.14 immediately.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of pi after step 2?

A 3.14159

B undefined

C 3.14

D Error

💡 Hint

Check the 'Value' column for pi at step 2 in the execution_table.

At which step does the program stop due to an error?

A Step 1

B Step 3

C Step 2

D No error

💡 Hint

Look at the 'Result/Output' column in the execution_table for error messages.

If we remove the reassignment line, what will be the output at step 2?

A 3.14

B undefined

C Error

D Nothing

💡 Hint

Refer to the output at step 2 in the execution_table when pi is printed.

Concept Snapshot

const variableName = value;
- Declares a constant variable.
- Must assign value at declaration.
- Cannot reassign later (error if tried).
- Use for values that should not change.

Full Transcript

This example shows how to declare a constant variable in JavaScript using const. First, we declare pi with the value 3.14. Then we print pi, which outputs 3.14. Finally, we try to change pi to 3.14159, but this causes an error because const variables cannot be reassigned. The execution stops at this error. Remember, const variables must be assigned a value when declared and cannot be changed later.