What is optional parameter?

A parameter that may not be provided.

What is default parameter?

A parameter with a default value.

Default parameters are more predictable.

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What are Optional Parameters?

Optional parameters allow you to define function parameters that may or may not be provided when the function is called.

Optional Parameter Syntax

TypeScriptRead-only

function greet(name?: string) {
  return name || 'Guest';
}

function greet(name?: string) {
  return name || 'Guest';
}

Default Parameters

Default parameters assign a default value when no argument is passed.

TypeScriptRead-only

function greet(name: string = 'Guest') {
  return name;
}

function greet(name: string = 'Guest') {
  return name;
}

Optional vs Default

Feature	Optional	Default
Value Required	No	No
Default Value	No	Yes
Usage	Flexible input	Predefined fallback

Combining Both

TypeScriptRead-only

function greet(name?: string, age: number = 18) {
  return `${name || 'Guest'} - ${age}`;
}

function greet(name?: string, age: number = 18) {
  return `${name || 'Guest'} - ${age}`;
}

Parameter Order Rules

Optional parameters must come after required parameters, while default parameters can be placed flexibly but should follow best practices.

Best Practices

Place optional parameters at the end
Use default values for predictable behavior
Avoid too many optional parameters
Keep function signatures simple

Common Mistakes

Wrong parameter order
Confusing optional with default
Overusing optional parameters
Not handling undefined values properly

Conclusion

Optional and default parameters improve flexibility in TypeScript functions while maintaining clarity and type safety.

Feature

Optional

Default

Value Required

Default Value

Yes

Usage

Flexible input

Predefined fallback

TypeScript Optional & Default Parameters

TypeScript Optional & Default Parameters

What are Optional Parameters?

Optional Parameter Syntax

Default Parameters

Optional vs Default

Combining Both

Parameter Order Rules

Best Practices

Common Mistakes

Conclusion

Try it yourself

Test Your Knowledge

Frequently Asked Questions

Need help?

TypeScript Optional & Default Parameters

TypeScript Optional & Default Parameters

What are Optional Parameters?

Optional Parameter Syntax

Default Parameters

Optional vs Default

Combining Both

Parameter Order Rules

Best Practices

Common Mistakes

Conclusion

Try it yourself

Test Your Knowledge

Frequently Asked Questions

Need help?