tsGuard

TypeScript Type Guard Library.

import { TSGuard } from './tsGuard';

Simple Types

This prevents case-sensitivity errors, and typos.

method(example: string | number) {
    var example: string | number = '';
    if (TSGuard.isNumber(example)) {
        // example: number
        console.log(example.toFixed());
    } else {
        // example: string
        console.log(example.length);
    }
}

Simple Custom Type Guards

isNumber(item: any)

isString(item: any)

isObject(item: any)

Structures

This allows you to check that a type matches some structure.

method(example: Structure | AlternateStructure) {
    if (TSGuard.isStructure<Structure>(example, { name: ''})) {
        // example: Structure
        console.log(example.name);
    } else {
        // example: AlternateStructure
        console.log(example.n)
    }
}

You can narrow down from any type to a structural type...

method(example: any) {
    if (TSGuard.isStructure<{age: number}>(example, { age: 1})) {
        // example: { age: number }
        console.log(example.age);
    } else {
        // example: any
        console.log(JSON.stringify(example))
    }
}

And you can catch subsets of types, including simple types...

export interface NumberLike {
    toFixed(): string;
}

// The above interface only has one method that matches number, so it is "Number Like"...

// Here is the structural check in use, happily allowing any type with toFixed(): string into the "if"

method(example: number | NumberLike | {}) {
    if (TSGuard.isStructure<{toFixed(): string}>(example, { toFixed: () => '' })) {
        // example: number | NumberLike
        console.log(example.toFixed());
    } else {
        // example: {}}
        console.log(JSON.stringify(example))
    }
}

Structural Custom Type Guards

isStructure<T>(item: any, matcher: T)