ts-narrow
Typescript type predicates with no dependencies.
This library is not supposed to be a schema validator, or a object validator, so it doesn't throw any errors and will always return a boolean result. You should use this library as a quick helper to narrow from more generic types, to something that you can work with.
For example:
Here you're receiving an unknown object, which you can't work with on typescript.
By the time the program evaluates the 'if' condition as true, constant a type will be narrow, meaning that now you can be sure that constant a is a object and has a prop b of type number.
This program will enter inside 'if' condition only if constant a matches exactly this condition, and your IDE will respect these types.
Under the hood, it uses advanced user defined types to bring the best of two worlds: a fast runtime check within a amazing developer experience.
Library methods
hasElementAt
Checks if target is an array and it has an element on a specific position.
hasElementAtOf
Checks if target is an array and it has an element on a specific position. Can be composed to check the type of the element.
hasProp
Checks if target is an object and it has a specific property.
hasPropOf
Checks if target is an object and it has a specific property. Can be composed to check the type of the property.
isArray
Checks if target is an array.
isArrayOf
Checks if target is an array. Can be composed to check the type of all elements.
isEnum
Checks if target is a typescript enum.
isEnumOf
Checks if target is a specific enum.
isEnumValueOf
Checks if target is a value of a specific enum.
isNumber
Checks if target is a number.
isObject
Checks if target is an object.
Please notice that null is a valid javascript object.
isOneOf
Checks if target is one of passed arguments.
isUnionOf
Checks if target is all of passed arguments.
isString
Checks if target is a string.
isRecordOf
Checks if target is an object and it has all its properties with the same passed type.
ensure
Throws if target is null or undefined.
Can receive an optional message or anything that extends Error to customize the message to be throw.
isLiteral
Checks if target is a literal with specific value.
isObjectOf
Checks if target is a object with specific shape.
Can be composed to check the type of each property individually by using a NarrowFunc.
It doesn't care about extra properties.
isInstanceOf
Checks if target is an instance of a class.
assert
Throws if passed condition is not true. Can receive a optional message or anything that extends Error to customize the message to be throw.
assertOf
Throws if passed condition is not true. It also narrows argument to have matched condition type. Can receive a optional message or anything that extends Error to customize the message to be throw.
isOneStringLiteralOf
Checks if string is one of strings passed in a list.
isBoolean
Checks if target is a boolean.
ensureOf
Throws if target returns false from a NarrowFunc.
isTruthy
Check if target is not null, undefined.