Call a custom GAS function from external URL

Solution 1:

• In either a "stand alone" or bound Apps Script file add a doGet(e) function.
• Publish the Apps Script file as a Web App.
• Get the published URL of the Web App.
• Add a search string parameter to the end of the URL.

You can add search string parameters to the URL of the published Wep App.

Here is an example:

https://script.google.com/macros/s/[ID]/exec?searchStringName=functionOne

The search string is at the end of the URL, after exec. You must add a question mark after exec and then name=value

url/exec?name=value

Where name and value will be replaced with your choices.

Put the event argument (denoted by the letter "e") into the doGet(e) function, not the function you want used.

function doGet(e) {
  var passedString,whatToReturn;

  passedString = e.parameter.searchStringName;
  if (passedString === 'functionOne') {
    whatToReturn = functionOne();  //Run function One
  };

  return ContentService.createTextOutput(whatToReturn);
};

function functionOne() {
  var something;

  //. . . . Code;
  something = code here;
  return something;
};

The above code is for a GET request. If you want to use a POST request, don't use a search string in the URL. For a POST request, you will send information in the payload. You'll still use e.parameter to access the data sent, but whatever is in e.parameter will be an object with key/value pairs. You'll need to know what the key (property) name is that was sent in the object.

For an explanation on URL Parameters, see this documentation:

URL Parameters