The Tool Desk
Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →iTechGuides is reader-supported. When you buy through links on our site, we may earn an affiliate commission. As an Amazon Associate I earn from qualifying purchases. Learn more
In TypeScript, any turns off type checking for a value: you can access properties, call it, and assign it to other types without the compiler verifying those operations. Use it sparingly at deliberate boundaries, such as a temporary step in a JavaScript migration. For data whose shape is not yet known, prefer unknown and narrow it before use.
What does any do in TypeScript?
any is an opt-out from type checking. A value typed any can be used as though it had any type, so TypeScript accepts operations it could not verify. Values derived from it can also become any, allowing the unchecked type to spread through the program.
For example, the compiler accepts this assignment even though the function returns a string where the code expects a number:
function readExternalValue(): any {
return JSON.parse('{"count":"not a number"}');
}
const count: number = readExternalValue(); // Compiles, but the value is not checked as a number.The compiler has accepted the assignment; that does not establish that the runtime value is a number. TypeScript’s Handbook explains the behavior of any and cautions that type safety is a main reason to use TypeScript, so any should be avoided when it is not necessary.
#1 Best Overall
When should you use any?
The TypeScript Handbook recognizes any as useful when working with existing JavaScript, code outside TypeScript, or a third-party library whose types are unavailable. It can also serve as temporary scaffolding while a JavaScript project is being converted: the migration can proceed before every value has a precise type.
Keep such uses explicit and narrowly scoped. Each one marks a place where the compiler cannot provide type safety. As the codebase or its type information improves, replace the annotation with a useful type or with unknown if the value’s shape remains uncertain. The TypeScript migration guide discusses using any during conversion and tightening checks as the work progresses.
Rank #2
- TypeScript implements a superset of syntax for strictly typed development, facilitating deep static analysis and enhanced development environment integration. The compiler translates source into standard script formats, ensuring parity across any runtime.
- TypeScript is ideal for front-end developers, full-stack engineers, and software architects who build large-scale web applications. It serves those looking to improve code excellence, reduce bugs through static checking, and maintain complex projects more.
- Lightweight, Classic fit, Double-needle sleeve and bottom hem
any vs. unknown: which should you choose?
Both types can hold a value of any kind, but they make different promises to the code that uses it. any permits unchecked operations; unknown represents uncertainty and requires you to establish what the value is before treating it as a specific type.
Free tools Windows power users keep installed
One-click scans. No signup required.
| Question | any |
unknown |
|---|---|---|
| Can you access properties or call the value without a check? | Yes; the compiler allows unchecked operations. | No; narrow the value before using it as a specific type. |
| Can the type propagate through derived values? | Yes; it can spread unchecked. | It remains uncertain until narrowed. |
| Best fit | A deliberate, limited escape hatch, such as temporary migration scaffolding. | A value with an unknown shape, or one passed through without inspection. |
For example, narrow an unknown value before treating it as a number:
function readExternalValue(): unknown {
return JSON.parse('{"count":3}');
}
const value = readExternalValue();
if (typeof value === 'number') {
// value is narrowed to number here.
}This illustrates type narrowing, not complete JSON validation. A check for a number would not establish that an object has a particular structure. For external input such as JSON, static TypeScript annotations alone do not validate the data at runtime; validate the shape before relying on it.
The TypeScript Do’s and Don’ts guidance recommends unknown when a type is not known or a value will be passed through without interaction. It also recommends void, rather than any, for a callback whose return value is intentionally ignored.
How do you catch implicit any?
An implicit any occurs when TypeScript cannot infer a type and would otherwise fall back to any. Enable noImplicitAny to have the compiler report those cases. The broader strict option enables noImplicitAny along with other strict checks.
Recommended Free Tools
{
"compilerOptions": {
"strict": true
}
}You can enable just the inference check instead by setting "noImplicitAny": true in compilerOptions. See the official noImplicitAny TSConfig reference.
Best Value
This setting does not prohibit explicit annotations such as : any. If a team wants to discourage or ban explicit any, compiler settings alone are not enough; add an appropriate lint rule or code-review policy.
How should you handle any during a JavaScript migration?
- Use it only where it unblocks conversion. An explicit
anycan be a temporary bridge when existing code or missing type information makes a more precise annotation impractical. - Turn on
noImplicitAnyas you adopt stricter checks. It identifies cases where the compiler would inferany; it does not remove explicit annotations. - Revisit each explicit annotation as understanding improves. Replace it with a specific type when the shape is known, or use
unknownwhen it is not yet known and should be narrowed.
The official migration guidance presents stricter checks as part of gradual adoption. Treat each explicit any as a visible exception to type safety rather than as a type that has been verified.
Why are catch variables sometimes unknown?
JavaScript can throw values other than Error objects, so a catch block should not assume that every caught value has a message property. TypeScript 4.4 introduced the useUnknownInCatchVariables option, which makes catch variables default to unknown. The option is enabled by strict.
Narrow the value before accessing error-specific properties:
try {
// Operation that may throw.
} catch (error) {
if (error instanceof Error) {
console.error(error.message);
}
}The TypeScript 4.4 release notes describe this setting and demonstrate narrowing with instanceof Error.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
