Added Support for Custom Sheet Functions

Author: labnol

.eslintignore

@@ -1,3 +1,4 @@
 dist
 node_modules
-google_apps_script
+google_apps_script
+functions

FUNCTIONS.md

@@ -0,0 +1,30 @@
+# Custom Functions in Google Sheets
+
+Google Sheets has a number of built-in formula functions such as `=SUM()` that enable quick calculations on spreadsheet data. Custom functions are simply functions that you define yourself, using Apps Script. Once you've defined a custom function, you can use it anywhere in your spreadsheet, just like a built-in function.
+
+This section shows you how to create a custom Sheet functions locally and upload it to your Apps Script project.
+
+1. Create a new file in the function folder and append a .js extension to the file name.
+
+2. Write the sheets function in the new file and append a JSDoc comment blocks to explain what your function will do. [See example](./functions/currency.js)
+
+In this comment, you can identify two parts: the function description and annotations that describe the function's parameters and return type.
+
+`@param:` You can use the @param annotation to describe each parameter passed into the function.
+
+`@return:` You can utilize the @return annotation to describe what the function returns.
+
+`@customfunction:` You should always add `@customfunction` in any custom function's doc comment. This annotation notifies Sheets to autocomplete your custom function just as Sheets autocomplete built-in functions when you type a function name in a cell as seen below:
+
+Save the file. The functions file will automatically get uploaded to the Apps Script project with the comment block intact.
+
+The comment block is required for Google Sheets to autocomplete for custom functions much like for built-in functions. As you type a function name in a cell, you will see a list of built-in and custom functions that matches what you enter.
+
+### Guidelines for Naming custom functions
+
+Before writing your own custom function, there are a few guidelines to know.
+
+- The name of a custom function must be distinct from the names of built-in functions like SUM().
+- The name of a custom function cannot end with an underscore (\_), which denotes a private function in Apps Script.
+- The name of a custom function must be declared with the syntax function myFunction(), not var myFunction = new Function().
+- Capitalization does not matter, although the names of spreadsheet functions are traditionally uppercase.

README.md

@@ -78,6 +78,10 @@ The default `.claspignore` file in the Apps Script Starter kit will push all the
 
 Create a new repository in Github and make a note of the URL of the new repository. Next, open the terminal and run the above commands to push your Apps Script project to Github.
 
+## Custom Google Sheet function
+
+Please read [the tutorial](./FUNCTIONS.md) on how to write custom functions for Google Sheets using Apps Script.
+
 ## :fire: Meet the Developer
 
 <img align="left" width="100" height="100" src="https://pbs.twimg.com/profile_images/1144978512832368640/Ej7Zz7E9_400x400.jpg">

functions/currency.js

@@ -0,0 +1,11 @@
+/**
+ * Converts US dollars to Indian Rupee.
+ *
+ * @param {number} dollars The total number of dollars.
+ * @return {number} indianRupee The converted total of Indian Rupeet.
+ * @customfunction
+ */
+function USDTOINR(dollars){
+    var indianRupee = dollars * 76;
+    return indianRupee;
+  }

functions/double.js

@@ -0,0 +1,16 @@
+/**
+ * Multiplies the input value by 2.
+ *
+ * @param {number} input The value or range of cells to multiply.
+ * @return The input multiplied by 2.
+ * @customfunction
+ */
+function DOUBLE(input) {
+    if (input.map) {
+        return input.map(DOUBLE); // Recurse over array if so.
+    } else {
+        return input * 2;
+    }
+}
+
+

package-lock.json

@@ -29,29 +29,29 @@
     "crypto-js": "3.1.9-1"
   },
   "devDependencies": {
-    "@babel/core": "^7.10.2",
-    "@babel/plugin-proposal-object-rest-spread": "^7.10.1",
-    "@babel/plugin-proposal-optional-chaining": "^7.10.1",
-    "@babel/preset-env": "^7.10.2",
+    "@babel/core": "^7.10.3",
+    "@babel/plugin-proposal-object-rest-spread": "^7.10.3",
+    "@babel/plugin-proposal-optional-chaining": "^7.10.3",
+    "@babel/preset-env": "^7.10.3",
     "@google/clasp": "^2.3.0",
     "@types/google-apps-script": "^1.0.14",
     "babel-eslint": "^10.1.0",
     "babel-loader": "^8.1.0",
     "babel-plugin-add-module-exports": "^1.0.2",
     "clean-webpack-plugin": "^3.0.0",
-    "copy-webpack-plugin": "^6.0.1",
+    "copy-webpack-plugin": "^6.0.2",
     "cross-env": "^7.0.2",
-    "eslint": "^7.1.0",
-    "eslint-config-airbnb-base": "^14.1.0",
+    "eslint": "^7.3.1",
+    "eslint-config-airbnb-base": "^14.2.0",
     "eslint-config-prettier": "^6.11.0",
     "eslint-loader": "^4.0.2",
     "eslint-plugin-googleappsscript": "^1.0.3",
-    "eslint-plugin-import": "^2.20.2",
-    "eslint-plugin-prettier": "^3.1.3",
-    "gas-webpack-plugin": "^1.0.2",
+    "eslint-plugin-import": "^2.22.0",
+    "eslint-plugin-prettier": "^3.1.4",
+    "gas-webpack-plugin": "^1.0.3",
     "prettier": "^2.0.5",
-    "terser-webpack-plugin": "^3.0.2",
+    "terser-webpack-plugin": "^3.0.6",
     "webpack": "^4.43.0",
-    "webpack-cli": "^3.3.11"
+    "webpack-cli": "^3.3.12"
   }
 }

package.json

@@ -83,6 +83,11 @@ module.exports = {
           from: `${src}/../appsscript.json`,
           to: destination,
         },
+        {
+          from: `${src}/../functions/*.js`,
+          to: destination,
+          flatten: true,
+        },
       ],
     }),
     new GasPlugin({