All items in an array to uppercase?

.toUpperCase is a string method, if you use it with a array it doesn't run but are you sure that you need the array inStock in uppercase? If you look your code doesn't use it

Hi, I think you need to loop through the elements of the array.

for (let i = 0; i < stock.length; i++) {
 stock[i] = stock[i].toUpperCase();
}

If you need to make sure all the elements are strings, add an if statement with the condition typeof stock[i] === 'string'

for (let i = 0; i < stock.length; i++) {
    if (typeof stock[i] === 'string') {
        stock[i] = stock[i].toUpperCase();
    }
}

Does it fit your needs ?

Raphaël

Another useful array method is map. It basically loops through all elements of an array, applies a function to them and pushes the results into a new array:

function toUpper(item) {
    return item.toUpperCase();
}

var stockUppercase = inStock.map(toUpper);

Note that inside of map, we are not calling toUpper - there is no () after it. The map function will call toUpper itself on every element in the array.

If you want to get extra fancy, you can inline the function definition of toUpper:

var stockUppercase = inStock.map(function toUpper(item) {
    return item.toUpperCase();
});

Naming the function is optional:

var stockUppercase = inStock.map(function (item) {
    return item.toUpperCase();
});

Since version 6 of JavaScript, there is also a shorthand notation for defining functions:

var stockUppercase = inStock.map(item=> item.toUpperCase());

Don't get confused with this, it's is perfectly fine to type a simple for-loop for this kind of operation, as shown by Raphaël.