Tuple with fixed length and types in Typescript - Step-by-Step Execution

Concept Flow - Tuple with fixed length and types

Define tuple type with fixed length and types

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Create tuple variable with matching values

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Access tuple elements by index

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Use tuple elements with known types

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TypeScript checks length and types at compile time

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Code runs with fixed tuple structure

This flow shows how TypeScript defines a tuple with fixed length and types, creates a matching tuple, accesses elements, and enforces type checks.

Execution Sample

Typescript

const person: [string, number] = ["Alice", 30];
console.log(person[0]);
console.log(person[1]);

Defines a tuple with a string and a number, then prints each element.

Execution Table

Step	Action	Evaluation	Result
1	Define tuple type [string, number]	TypeScript sets person as tuple of string and number	person: [string, number]
2	Assign ['Alice', 30] to person	Check length=2 and types string, number	person = ['Alice', 30] passes type check
3	Access person[0]	Retrieve first element	"Alice"
4	Access person[1]	Retrieve second element	30
5	Print person[0]	Output to console	Alice
6	Print person[1]	Output to console	30
7	Try assigning wrong type or length	TypeScript error	Compilation error (not shown at runtime)

💡 Execution ends after printing tuple elements; TypeScript enforces tuple type at compile time.

Variable Tracker

Variable	Start	After Assignment	Final
person	undefined	['Alice', 30]	['Alice', 30]

Key Moments - 3 Insights

Why does TypeScript give an error if I add an extra element to the tuple?

Because the tuple type [string, number] expects exactly two elements. Adding more breaks the fixed length rule, as shown in step 7 of the execution_table.

Can I put a number in the first position of the tuple?

No, the first position must be a string as defined by the tuple type. Assigning a number there causes a type error, as TypeScript checks types at assignment (step 2).

What happens if I access an index outside the tuple length?

TypeScript will warn at compile time that the index is out of range, preventing runtime errors. This is because the tuple length is fixed (step 3 and 4 show valid indices).

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of person[1] at step 4?

A "Alice"

B 30

C undefined

D Type error

💡 Hint

Check the 'Evaluation' and 'Result' columns at step 4 in the execution_table.

At which step does TypeScript check the tuple length and types?

A Step 2

B Step 1

C Step 5

D Step 7

💡 Hint

Look for the step where assignment and type checking happen in the execution_table.

If you try to assign ['Bob', 25, true] to person, what happens according to the execution_table?

A It works fine

B Only first two elements are assigned

C TypeScript error due to extra element

D Runtime error

💡 Hint

Refer to step 7 in the execution_table about wrong length or types.

Concept Snapshot

Tuple with fixed length and types in TypeScript:
- Syntax: const var: [type1, type2] = [val1, val2];
- Length and types fixed at compile time
- Access elements by index with known types
- TypeScript errors if length or types mismatch
- Useful for fixed structured data

Full Transcript

This example shows how TypeScript uses tuples to store fixed-length arrays with specific types. We define a tuple person with a string and a number. When assigning values, TypeScript checks that the array has exactly two elements: a string first and a number second. Accessing elements by index returns values with the expected types. If we try to assign more elements or wrong types, TypeScript gives errors before running the code. This helps catch mistakes early and keeps data structured.