# Custom function quickstart

You can use Google Apps Script to write a custom function, then use it in Google Sheets just like a built-in function.

The following quickstart sample creates a custom function that calculates the sale price of discounted items. The sale price is formatted as US dollars.

## Objectives

• Set up the script.
• Run the script.

## Prerequisites

To use this sample, you need the following prerequisites:

• A Google Account (Google Workspace accounts might require administrator approval).
• A web browser with access to the internet.

## Set up the script

1. Create a new spreadsheet.
2. From within your new spreadsheet, select the menu item Extensions > Apps Script.
3. Delete any code in the script editor and paste in the code below. Then click Save .

```/**
* Calculates the sale price of a value at a given discount.
* The sale price is formatted as US dollars.
*
* @param {number} input The value to discount.
* @param {number} discount The discount to apply, such as .5 or 50%.
* @return The sale price formatted as USD.
* @customfunction
*/
function salePrice(input, discount) {
let price = input - (input * discount);
let dollarUS = Intl.NumberFormat("en-US", {
style: "currency",
currency: "USD",
});
return dollarUS.format(price);
}
```

## Run the script

1. Switch back to your spreadsheet.
2. In a cell, enter `=salePrice(100,.2)`. The first parameter represents the original price and the second parameter represents the discount percentage. If you're in a location that uses decimal commas, you might need to enter `=salePrice(100;0,2)` instead.

The formula that you enter in the cell runs the function in the script you created in the previous section. The function results in a sale price of `\$80.00`.

## Next steps

To continue learning about how to extend Sheets with Apps Script, take a look at the following resources:

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[{ "type": "thumb-up", "id": "easyToUnderstand", "label":"Easy to understand" },{ "type": "thumb-up", "id": "solvedMyProblem", "label":"Solved my problem" },{ "type": "thumb-up", "id": "otherUp", "label":"Other" }]