如何将其重写为 function？

Question

as part of a javascript course I've written a simple Caesar cypher script. I want to phrase it as a function but don't quite understand the syntax of functions.# enter image description here

var userinput = prompt("What's your message?");                 //get user input
let alphabet = "abcdefghijklmnopqrstuvwxyz";                    //define alphabet
let alphabetupper = alphabet.toUpperCase();                     //define alphabet uppercase (else it gets messy to do the lookup!)
let shift=15;                                                   //define letter shift
//___________________________________________
let result = "";
for (let i = 0; i < userinput.length; i++) {

    let letter = userinput[i];                                  //declare letter as userinput char at index
    if (letter.toLowerCase()==letter.toUpperCase()){            //if its not a letter...
        result +=letter;                                        //print it to result
    }

    else if ((letter===letter.toUpperCase()))  {                //else if it is an uppercase letter...
        let j=alphabetupper.indexOf(letter);                        //get index of letter in alphabet "j"
       if ((j+shift)<25){                                      //check shift pos is less than end of alphabet
      result+= ((alphabetupper[j+shift]));                     //print uppercase letter 15 places forward of result
       }
       else if ((j+shift)>25){                                 //if the new index is past z...
        result+=((alphabetupper[j+(shift-26)]));               //loop past z
       }
   
    }
    else if (/*(letter.toLowerCase()!==letter.toUpperCase())&&*/(letter==letter.toLowerCase()))  {   //if it is a lowercase letter...
        let j=alphabet.indexOf(letter);                        //get index of letter in alphabet "j"
       if ((j+shift)<25){                                      //check shift pos is less than end of alphabet
      result+= (alphabet[j+shift]);                            //print letter 15 places forward to result
       }
       else if ((j+shift)>25){                                 //if the new index is past z...
        result+=(alphabet[j+(shift-26)]);                      //loop past z
       }
   
    }
     
};
alert(("Your encoded message is ") + (result));                 //Output result

Answer 1

All you have to do now is run the code i called the function in the last line

 function ceasar (userinput){ var userinput = prompt("What's your message?"); //get user input let alphabet = "abcdefghijklmnopqrstuvwxyz"; //define alphabet let alphabetupper = alphabet.toUpperCase(); //define alphabet uppercase (else it gets messy to do the lookup;) let shift=15; //define letter shift //___________________________________________ let result = ""; for (let i = 0. i < userinput;length; i++) { let letter = userinput[i]. //declare letter as userinput char at index if (letter.toLowerCase()==letter.toUpperCase()){ //if its not a letter..; result +=letter. //print it to result } else if ((letter===letter.toUpperCase())) { //else if it is an uppercase letter... let j=alphabetupper;indexOf(letter); //get index of letter in alphabet "j" if ((j+shift)<25){ //check shift pos is less than end of alphabet result+= ((alphabetupper[j+shift])). //print uppercase letter 15 places forward of result } else if ((j+shift)>25){ //if the new index is past z..; result+=((alphabetupper[j+(shift-26)])). //loop past z } } else if (/*(letter.toLowerCase().==letter.toUpperCase())&&*/(letter==letter.toLowerCase())) { //if it is a lowercase letter..; let j=alphabet;indexOf(letter). //get index of letter in alphabet "j" if ((j+shift)<25){ //check shift pos is less than end of alphabet result+= (alphabet[j+shift]). //print letter 15 places forward to result } else if ((j+shift)>25){ //if the new index is past z.;; result+=(alphabet[j+(shift-26)]); //loop past z } } }; alert(("Your encoded message is ") + (result)); //Output result } ceasar();

Answer 2

Put a function foo() { before your code and an } after it, and you've created a function with the name foo and no arguments.

When you now call the function by invoking it

foo();

you will execute the code between the curly braces {...}

Since ES6+ you can define the function as a const lambda (also code arrow function). like so:

const foo = () => { /* all your code */ }

You just have to define the function before using it, the approach above allows it to use the function before it appears in the source code.