I was trying to implement recaptcha on my website, so I created a callback function using javascript which should be executed when a user submits a successful captcha response:

<script>
   function onSubmit = function(token) {
      document.getElementById("form-signin").submit();
   }
</script>

But always got this error SyntaxError: missing ( before formal parameters when using Firefox.

When using Google Chrome, I got this error instead: Uncaught SyntaxError: Unexpected token =

Both browsers indicate that the error is located at function onSubmit = function(token) {, but I don't know why this happened.

Can anyone be so kind as to tell me what is wrong?

I was trying to implement recaptcha on my website, so I created a callback function using javascript which should be executed when a user submits a successful captcha response:

<script>
   function onSubmit = function(token) {
      document.getElementById("form-signin").submit();
   }
</script>

But always got this error SyntaxError: missing ( before formal parameters when using Firefox.

When using Google Chrome, I got this error instead: Uncaught SyntaxError: Unexpected token =

Both browsers indicate that the error is located at function onSubmit = function(token) {, but I don't know why this happened.

Can anyone be so kind as to tell me what is wrong?

• javascript
• function

Share Improve this question Follow asked Jan 7, 2017 at 13:47 GPrazGPraz 30844 silver badges1313 bronze badges 2

• you should try var onSubmit = – Deep Commented Jan 7, 2017 at 13:49
• How I got this error: I didn't get enough sleep and for some reason I though I can use dashes (mathematical operators for subtraction) in function names. For anyone wondering and stumbling upon the same error, you can't (obviously; it's subtraction). – jg6 Commented Aug 25, 2020 at 21:03

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2 Answers 2

Sorted by: Reset to default 2

There are two basic ways to declare a named function:

function onSubmit(token){
    document.getElementById("form-signin").submit();
}

Or:

var onSubmit = function(token){
    document.getElementById("form-signin").submit();
};

In your case, just go with the first.

function some_identifier can start either a function declaration or a function expression. Either way, the next characters must be ( then any argument definitions, then ).

If you want to assign the result of evaluating a function expression to a variable, as you are trying to do here, then you must declare the variable in the normal way (i.e. with the var keyword, unless you have declared it already, or are not using strict mode and want to create a global).

So either:

function onSubmit(token) {
  document.getElementById("form-signin").submit();
}

or

var onSubmit = function(token) {
  document.getElementById("form-signin").submit();
}