javascript（Google Apps脚本）声明变量

Question

I have written a code. To run the code I have declared quite a few variables. Now that I finished, I realised that I did not have to declare the variables as I can call on what the variable is supposed to call for directly within the function.

Example:

function test() {
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = ss.getActiveSheet();
  var date = Utilities.formatDate(new Date(), "GMT", "dd-MMM-yyyy");
  sheet.appendRow(date);
}

I could have not declared date and written this:

function test() {
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = ss.getActiveSheet();
  sheet.appendRow(Utilities.formatDate(new Date(), "GMT", "dd-MMM-yyyy"));
}

Which of those is considered best practice and better for performance of app?

Thanks

Answer 1

The effect on performance will be negligible. You should write it the way that is most readable. In your case that is debatable, but I like declaring the date variable since it makes the subsequent line much shorter and less overwhelming.

A case where it could affect performance would be if you were consuming the date in multiple locations. Then, you would want to declare a variable. For example...

function test() {
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = ss.getActiveSheet();
  sheet.appendRow(Utilities.formatDate(new Date(), "GMT", "dd-MMM-yyyy"));
  somethingElse(Utilities.formatDate(new Date(), "GMT", "dd-MMM-yyyy"));
}

Aside from violating the DRY principle , the above hurts performance because you are doing the work twice (creating a Date object and formatting it).

In summary, if you are only consuming the value once, you don't need to make it a variable, but you should if it improves readability.