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SyntaxError: function statement requires a name

The JavaScript exception "function statement requires a name" occurs when there is a function statement in the code that requires a name.

Message​

SyntaxError: Function statements require a function name (V8-based)
SyntaxError: function statement requires a name (Firefox)
SyntaxError: Function statements must have a name. (Safari)

Error type​

What went wrong?​

There is a function statement in the code that requires a name. You'll need to check how functions are defined and if you need to provide a name for it, or if the function in question needs to be a function expression, an IIFE, or if the function code is placed correctly in this context at all.

Examples​

Statements vs. expressions​

A function statement (or function declaration) requires a name. This won't work:

function () {
  return "Hello world";
}
// SyntaxError: function statement requires a name

You can use a function expression (assignment) instead:

const greet = function () {
  return "Hello world";
};

If your function is intended to be an IIFE (Immediately Invoked Function Expression, which is a function that runs as soon as it is defined) you will need to add a few more braces:

(function () {
  // …
})();

Labeled functions​

Labels are an entirely different feature from function names. You can't use a label as a function name.

function Greeter() {
  german: function () {
    return "Moin";
  }
}
// SyntaxError: function statement requires a name

In addition, labeled function declarations themselves are a deprecated feature. Use regular function declarations instead.

function Greeter() {
  function german() {
    return "Moin";
  }
}

Object methods​

If you intended to create a method of an object, you will need to create an object. The following syntax without a name after the function keyword is valid then.

const greeter = {
  german: function () {
    return "Moin";
  },
};

You can also use the method syntax.

const greeter = {
  german() {
    return "Moin";
  },
};

Callback syntax​

Also, check your syntax when using callbacks. Braces and commas can quickly get confusing.

promise.then(
  function () {
    console.log("success");
  });
  function () {
    console.log("error");
}
// SyntaxError: function statement requires a name

Correct would be:

promise.then(
  function () {
    console.log("success");
  },
  function () {
    console.log("error");
  },
);

See also​