Google Apps Script Library Code Sample

A library is a script project whose functions can be reused in other scripts.

Warning: 

A script that uses a library doesn't run as quickly as it would if all the code were contained within a single script project. Although libraries can make development and maintenance more convenient, use them sparingly in projects where speed is critical. Because of this issue, library use should be limited in add-ons.

Library Code Example:
/***** CREATE TEST OBJECT *****/ function testLibr() { let librObjtTest = librFunctions(); var result1 = librObjtTest.getFunction('function1', 2); console.log("result1:", result1); var result2 = librObjtTest.getFunction('function2', 3); console.log("result2:", result2); } /***** COPY THE FOLLOWING CODES TO CLIENT SCRIPT *****/ // create the library object // assuming the library name is librSample let librObjtSample = librSample.librFunctions(); // fetch the custom function and pass the parameters let customFunction = (f, ...params) => { return customFunctions.getFunction(f, params); } /***** DEFINE LIBRARY FUNCTIONS *****/ /** * The custom librFunctions * @return {Object} The customFunctions Object. */ function librFunctions() { /** * A custom function that adds a number to itself * * @param {Number} a number * @return {Number} a number */ function func1(num) { if (typeof num != 'number') { return null; } return num + num; } /** * A custom function that multiply itself * * @param {Number} a number * @return {Number} a number */ function func2(num) { if (typeof num != 'number') { return null; } return num * num; } /** * Define function names */ let allFunctions = { function1: func1, function2: func2 }; /** * @param {string} functionName * @param {any[]} params */ let getFunction = (functionName, params) => { // Check if the function name exists, if not return some help information if (!allFunctions[functionName]) { return "help information\n on how to us this function" } return allFunctions[functionName](params); } return Object.freeze({ getFunction: getFunction }); }

Link to Library Code Example

Best practices

Here are some guidelines to follow when writing a library:

• Choose a meaningful name for your project since it's used as the default identifier when your library is included by others.
• If you want one or more methods of your script to not be visible (nor usable) to your library users, you can end the name of the method with an underscore. For example, myPrivateMethod_().
• Only enumerable global properties are visible to library users. This includes function declarations, variables created outside a function with var, and properties explicitly set on the global object. For example, Object.defineProperty() with enumerable set to false creates a symbol you can use in your library, but this symbol isn't accessible by your users.
• If you want your library users to make use of the script editor autocomplete and the automatically generated documentation, you must have JSDoc-style documentation for all your functions. 

Here's an example:

JSDOC-style Code Exampple:
/** * Raises a number to the given power, and returns the result. * * @param {number} base the number we're raising to a power * @param {number} exp the exponent we're raising the base to * @return {number} the result of the exponential calculation */ function power(base, exp) { ... }

Reference:

https://developers.google.com/apps-script/guides/libraries