google chrome - Is there such a thing as not enough arguments in JavaScript? Why? - Stack Overflow

admin管理员组

文章数量:1341457

In JavaScript, it is valid to not pass some arguments to some functions. They get treated as undefined which is essential to many functions' logic.

I've read about this error called "Not enough arguments". Is it standard? Why does it exist?

function foo(a) {
  // yada yada
}
try {
  foo();
} catch (e) {
  console.log(e.name);
}

^ this code didn't throw anything on Firefox and Chrome.

In JavaScript, it is valid to not pass some arguments to some functions. They get treated as undefined which is essential to many functions' logic.

I've read about this error called "Not enough arguments". Is it standard? Why does it exist?

function foo(a) {
  // yada yada
}
try {
  foo();
} catch (e) {
  console.log(e.name);
}

^ this code didn't throw anything on Firefox and Chrome.

• javascript
• google-chrome
• firefox
• error-handling

Share Follow asked Sep 17, 2013 at 18:00 batmanbatman 5,4001414 gold badges5656 silver badges8787 bronze badges 2

• 1 Actually, they bee undefined. – SLaks Commented Sep 17, 2013 at 18:01
• 1 Checking the ever-wise MDN, it seems this is a custom error you should throw if your function really needs those arguments. (I only found it in examples; I saw no reference to the error itself.) – Evan Davis Commented Sep 17, 2013 at 18:07

Add a ment  | 

4 Answers 4

Sorted by: Reset to default 8

I've read about this error called "Not enough arguments".

This is not a standard langauge-level error; it's an API-level error. That is, JavaScript generally does not care if the number of actual arguments passed to a function matches the function's formal arguments. However, a particular API written in JavaScript might care about number of arguments.

For example, Firefox's addEventListener function (part of Firefox's DOM API) can throw a "Not enough arguments" error because the specification for addEventListener is defined to expect at least two arguments.

You can test the number of actual arguments passed to a function with the arguments object:

function foo(a, b) {
    if(arguments.length < 2) {
        throw TypeError("Not enough arguments; two expected");
    }

    if(arguments.length > 2) {
        throw TypeError("Too many arguments; two expected");
    }

    if(arguments.length > 10) {
        throw TypeError("Way too many arguments; did you even read the docs?");
    }
}

Your code must detect the number of arguments and actively throw an error if you want argument mismatch to result in an error. This version of foo will throw a TypeError that gets caught in your catch block.

Remember, however, that the error has nothing to do with the number of formal arguments of foo. I could have defined it as function foo(a,b,c), but still enforced a two-argument requirement by checking arguments.

Arguements are always optional in javascript. But that doesn't mean they are optional for a specific API. Consider:

function foo(a) {
  if (a === undefined) {
    var e = {};
    e.name = "Not enough arguements";
    e.message = "All your base r belong to us.";
    throw e;
  } 
  // yada yada
}
try {
  foo();
} catch (e) {
  console.log(e.name);
}

Now it is a required parameter. This is the case on some default DOM methods, which is what you will find if you google that exception.

Programmer-defined JavaScript functions have variable arity and arity is not strictly enforced (although there are ways to do it). However, native functions can enforce arity. For example, addEventListener requires two arguments: a string representing the event, and an event handler. If both arguments are not provided, you can get the "Not enough arguments" error. As I mentioned before, you can throw this error yourself if you require a specific number of parameters.

However, this is not strictly enforced. In Chrome, you can supply none, or only one parameter to addEventListener, and no errors will be reported. However, Firefox is stricter and will spit out the "Not enough arguments" error.

The reason this error exists is because executing the function will not make sense if all arguments are not provided. Of course, then one wonders why Chrome doesn't spit out an error.

"Not enough arguments" is shown only by Firefox when you are attempting to call standard DOM manipulation methods with arguments of wrong type (such as String instead of Function).

Plain JavaScript has no such notion, and you can't get this error if using your own functions.

本文标签： google chromeIs there such a thing as not enough arguments in JavaScript WhyStack Overflow