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");
},
);