How to Check if string is in list in javascript

Question

I wanted to check if an ad was displayed on an allowed website using javascript. I used a methodology explained in that post Determine if string is in list in JavaScript.

Here is my code :

async function ImpCertification(tx) {

    Impression = await getAssetRegistry('org.example.basic.Impression')

    const source = Impression.PrintedSite

    whitelist = ["Youtube", "Google", "Facebook", "Twitter"]

    if (whitelist.indexOf(source) < 0) {
        // Checks if source in whitelist
        throw new Error ('This impression does not respect branding')
    }

    // Checks every necessary conditions to validate impression
    if (whitelist.indexOf(source) >=0) {
        // Save the old value of the asset.
        const oldValue = Impression.Valid;

        // Update the asset with the new value.
        Impression.Valid = true;

        // Get the asset registry for the asset.
        const assetRegistry = await getAssetRegistry('org.example.basic.transaction.ValidateImpression');
        // Update the asset in the asset registry.
        await assetRegistry.update(Impression);

        // Emit an event for the modified asset.
        let event = getFactory().newEvent('org.example.basic', 'Validation');
        event.asset = tx.asset;
        event.oldValue = oldValue;
        event.newValue = true;
        emit(event);
    }
    await null
}

Can someone tell me how to do this?

Answer 1

At first, make sure that the string that you pass to indexOf is an actual string:

typeof <your-string-variable> === 'string'

To check if a string is in your list I suggest using ES6 Array.prototype.includes() :

['a', 'b', 'c'].includes('b')

To check if a string is a substring of the strings in your list combine Array.prototype.includes()method with String.prototype.includes() method:

(I also used ES6 reduce there to simplify the expression)

['hello', 'world', 'my', 'name', 'is', 'johny', 'cash'].reduce((current, item) => current || item.includes('substring_to_search'), false);

Hope this helps :-)