TIL Avoiding dependencies in your helper functions

POSTED ON: Dec 20, 2021

TAGS: helpers javascript testing functional-programming

This is a impure function.

import VALID_VALUES_LIST from './constants';

function isValueValid( value ) {
    return VALID_VALUES_LIST.includes( value );
}

Why? Because it NEEDS VALID_VALUES_LIST to work. It depends on it.

One of the super powers of functional programming is pure functions.

function isValueValid( value, validValuesArray = [] ) {
    return validValuesArray.includes( value );
}

This is a pure function. You can pass any array in the second param.

Now in your testing library, all of these will work with zero dependencies.

expect( isValueValid( 'hulk', [ 'batman', 'superman' ] ) ).toBe( false );

expect( isValueValid( 'hulk', null ) ).toBe( false );

expect( isValueValid( 'hulk', [] ) ).toBe( false );

expect( isValueValid( 'hulk', [ 'iron man', 'hulk' ] ) ).toBe( true );

VIA
WordPress Block Testing

Related TILs

Tagged: helpers

• Next: TIL CSS pseudo-element first-letter, to make a Drop CapYou can add a drop cap to a paragraph by using the ::first-letter pseudo-element.
• Previous: TIL Find unused JavaScriptChrome's Coverage panel allows you to quickly locate JavaScript (and CSS) code that has — and has not — been used. To start, open Coverage from the More tools sub-menu in the DevTools menu