Warning: expression closures are deprecated

Warning. JavaScript execution won't be halted.

The non-standard expression closure syntax (shorthand function syntax) is deprecated and shouldn't be used anymore. This syntax has been removed entirely in bug 1083458 and scripts using it will throw a SyntaxError in newer versions of Firefox.

Expression closures omit curly braces or return statements from function declarations or from method definitions in objects.

var x = function () 1;

var obj = {
  count: function () 1
};

To convert the non-standard expression closures syntax to standard ECMAScript syntax, you can add curly braces and return statements.

const x = function () {
  return 1;
};

const obj = {
  count() {
    return 1;
  },
};

Alternatively, you can use arrow functions:

const x = () => 1;

Expression closures can also be found with getter and setter, like this:

var obj = {
  get x() 1,
  set x(v) this.v = v
};

With method definitions, this can be converted to:

const obj = {
  get x() {
    return 1;
  },
  set x(v) {
    this.v = v;
  },
};

• Arrow functions
• Method definitions