Why is my javascript function not returning true? [duplicate]

Question

I have a javascript function :

function isInSupplier(idsupplier) { suppliers.forEach(function(object) { if (object._id == idsupplier) { console.log("TRUE"); return true; }; }); return false;

I have a list of products, each have a suppliers. I want to make a list of unique suppliers, therefore is the supplier is already in my suppliers list i will not add a new one.

Here is my function to do so :

 console.log(isInSupplier(('<s:property value="supplier.id" />'))); if (!isInSupplier(('<s:property value="supplier.id" />'))) { suppliers.push(new supplier( ('<s:property value="supplier.id" />'), ('<s:property value="supplier.supplier_name" />'), ('<s:property value="supplier.type" />'), ('<s:property value="supplier.phone" />') )); }

And there is something i don't understand : even tho the console logs "TRUE" properly, the function doesn't return true. In my second block of code i have another console log; that always logs false.

What is it i'm missing ?

You return only from your closure. I.e forEach. Your external function only returns false and thats what you are seeing — Hanky Panky
– Hanky Panky, Commented Feb 20, 2016 at 18:09
You are returning true only inside the forEach() function. The function you are wondering about always returns false — baao
– baao, Commented Feb 20, 2016 at 18:11

Nina Scholz · Accepted Answer · 2016-02-20 18:14:59Z

Please change it to Array.prototype.some()

The some() method tests whether some element in the array passes the test implemented by the provided function.

function isInSupplier(idsupplier) { return suppliers.some(function(object) { if (object._id == idsupplier) { console.log("TRUE"); return true; }; }); }

or without console output

function isInSupplier(idsupplier) { return suppliers.some(function(object) { return object._id == idsupplier; }); }

Ah yes some was what I was looking for, but I can never remember the JS higher-order function names.

madox2 · Accepted Answer · 2016-02-20 18:23:12Z

forEach method takes function as a parameter. If you return inside it you wont return from outer function. You can use Array.prototype.some to make it work:

function isInSupplier(idsupplier) { return suppliers.some(function (object) { return object._id == idsupplier; }); }

If your environment supports ES6 you can utilize it with arrow function:

function isInSupplier(idsupplier) { return suppliers.some(o => o._id == idsupplier); }

David Deutsch · Accepted Answer · 2016-02-20 18:11:23Z

1

You are returning true from the function you pass to forEach, not from isInSupplier.

answered Feb 20, 2016 at 18:11

David Deutsch

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Comments

Andrew Marshall · Accepted Answer · 2016-02-20 18:12:55Z

Your return true returns the function passed to forEach, not isInSupplier. Instead you can use findIndex:

function isInSupplier(idsupplier) { var index = suppliers.findIndex(function(object) { return object._id == idsupplier; }); return index != -1 }

Or really probably better to use some as in Nina’s answer (I couldn’t remember the name so resorted to findIndex).

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