JavaScript closures function

问题

I am new to JavaScript and I currently studying closures. Below you can see my code that is supposed to print any given array with a specified separator between each element. The thing is that if i try to create an array and print it in the makePath() function, everything works just fine. But when I try to do the same in the main function, it just doesn't work. I also have one more problem when I try to join the separator with the array, The separator is printed at the end of the list and I don't want that.

var makePath;

function makePath(separator) {
  let comp = []
  return function(element)

  {
    comp.push(element)
    return comp.join(separator)
  }
}

var path0 = makePath("/");
path0("A");
path0("B");
path0("C");
console.log("path 0 is " + path0());


var main = function() {

  var path1 = makePath("/");

  path1("A");
  path1("B");
  path1("C");

  var path2 = makePath("-->");
  path2("Berlin");
  path2("San Francisco");
  path2("Vancouver");

  var path3 = makePath();
  path3("A");
  path3("B");
  path3("C");

  window.console.log("path 1 is " + path1());
  window.console.log("path 2 is " + path2());
  window.console.log("path 3 is " + path3());
}

The output is:

path 0 is A/B/C/

回答1:

Q1: Why the makePath functions in main() didn't work?
Ans: You only declare the main function, but haven't call it, just add main() in the end, it will work!

Q2: Why there's an additional separator at the end of your output string?
Ans: The problem is in here: console.log("path 0 is " + path0());.
You called an additional path0(), which makes your Array comp became ['A', 'B', 'C', ' ' ].

You can modify your code like this:

var path0 = makePath("/");
path0("A");
path0("B");
let finalResult = path0("C");
console.log("path 0 is " + finalResult);

Without the additional call, the result should work as you expected.

来源：https://stackoverflow.com/questions/52970559/javascript-closures-function

标签

javascript

function

closures