Async Validation

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Async Validation
If you have wondered how async validation works with Strickland, you will be delighted at how simple it is: a validator can use a Promise.
Similar to how validate normalizes a boolean into validation result with an isValid property, a Promise is normalized into a validation result with a validateAsync property. The normalized validateAsync property is a function that returns a Promise resolving to the async result.
Let's take a look at a usernameIsAvailable validator. Just like synchronous validators, async validators can resolve to either boolean results or validation results with isValid properties.
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import validate from 'strickland';
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​
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function usernameIsAvailable(username) {
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    return new Promise((resolve) => {
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        if (username === 'marty') {
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            // Resolve to an invalid validation result object
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            resolve({
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                isValid: false,
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                message: `"${username}" is not available`
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            });
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        }
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​
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        // Resolve to a boolean
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        resolve(true);
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    });
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}
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​
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const result = validate(usernameIsAvailable, 'marty');
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​
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result.validateAsync().then((asyncResult) => {
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/*
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    asyncResult = {
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        isValid: false,
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        value: 'marty',
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        message: '"marty" is not available'
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    }
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 */
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});
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When a validator returns a Promise, the normalized validation result will include isValid: false to indicate that the result is not (yet) valid.
Composition and formatResult
Resolving Async Validation
Last modified 1yr ago
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