Type Assertion And Predicate (Taap)
A lightweight zero dependency Typescript type checking library that coerces unknown value types. More concise and accurate than typeof checks or similar type checking methods.
📚 Docs ⚡ Demo 💻 Repo
🛠Getting Started
Install dependency
npm i taapImport and use methods
import { isArray } from 'taap';
const maybeArray: unknown = [];
if (typeof maybeArray === 'array') {
🚫 typeof [] === 'object'
} else if (isArray(maybeArray)) {
// `maybeArray` is now of type: `any[]`
✅ maybeArray.push(1);
}Optionally supply a return type
import { isArray } from 'taap';
const maybeArray: unknown = [1, 2, 3];
if (isArray<number>(maybeArray)) {
// `maybeArray` is now of type: `number[]`
maybeArray.filter((x) => x > 1);
}🔠Available Methods
📚Full documentation
Supports optional generic return type:
Fixed return type:
Other:
Index
Type aliases
TaapType
Functions
getType
-
Parameters
-
v: any
Returns "Array" | "Object" | "String" | "Date" | "RegExp" | "Function" | "Boolean" | "Number" | "BigInt" | "Null" | "Undefined"
-
isArray
-
Type parameters
-
T
Accepts a type to narrow the return type.
Default: to
any.
Parameters
-
val: any
Returns val is Array<T>
-
isBigInt
-
Determine if argument is a
BigInt.const maybeBigInt: unknown = BigInt(42); if (isBigInt(maybeBigInt)) { maybeBigInt === 42n; }Parameters
-
val: any
Returns val is BigInt
-
isBoolean
-
Determine if argument is a
boolean.const maybeBoolean: unknown = true; if (isBoolean(maybeBoolean)) { maybeBoolean === true }Parameters
-
val: any
Returns val is boolean
-
isDate
-
Determine if argument is a
Date.const maybeDate: unknown = new Date('August 19, 1975 23:15:30'); if (isDate(maybeDate)) { maybeDate.setFullYear(1969); }Parameters
-
val: any
Returns val is Date
-
isFunction
-
Determine if argument is a
Function.const maybeFunction: unknown = (x: any) => x; if (isFunction(maybeFunction)) { maybeFunction.call(...args) }Provide a specific type:
const maybeFunction: unknown = (x: number) => x.toString(); if (isFunction<(x: number) => string>(maybeFunction)) { maybeFunction(42) === '42' }Type parameters
-
T
Accepts a type to narrow the return type.
Parameters
-
val: any
Returns val is T
-
isNull
-
Determine if argument is
null.const maybeNull: unknown = 1; if (isNumber(maybeNull)) { maybeNull === null; }Parameters
-
val: any
Returns val is null
-
isNumber
-
Determine if argument is a
number.const maybeNumber: unknown = 1; if (isNumber(maybeNumber)) { maybeNumber + 2 === 3; }Parameters
-
val: any
Returns val is number
-
isObject
-
Determine if argument is an
Object.const maybeObject: unknown = { a: true }; if (isObject(maybeObject)) { // `maybeObject` will be considered a Record<string, any> maybeObject.someProp = true }Provide a specific type:
const maybeObject: unknown = { a: true }; if (isObject<{a: boolean}>(maybeObject)) { // maybeObject will be typed as `{ a: boolean }` maybeObject.a === true; }Type parameters
-
T: Record<string, any>
Accepts a type to narrow the return type.
Parameters
-
val: any
Returns val is T
-
isRegExp
-
Determine if argument is a
RegEx.const maybeRegExp: unknown = /\w+\s/g; if (isRegExp(maybeRegExp)) { const str = 'fee fi fo fum'; maybeRegExp.test('fee fi fo fum') === true }Parameters
-
val: any
Returns val is RegExp
-
isString
-
Determine if argument is a
string.const maybeString: unknown = 'ta,ap'; if (isString(maybeString)) { maybeString.split(',').join('') === 'taap' }Parameters
-
val: any
Returns val is string
-
isUndefined
-
Determine if argument is
undefined.const maybeUndefined: unknown = 1; if (isNumber(maybeUndefined)) { maybeUndefined === undefined; }Parameters
-
val: any
Returns val is undefined
-
Generated using TypeDoc
Determine if argument is an
Array.const maybeArray: unknown = [1]; if (isArray(maybeArray)) { // `maybeArray` will be considered an Array maybeArray.map(x => x) }Provide a specific type:
const maybeArray: unknown = [1]; if (isArray<number>(maybeArray)) { // `maybeArray` will be considered an Array and `x` will be considered a number maybeArray.map((x => x) // ` }