JavaScript "Uncaught TypeError: object is not a function" associativity question_问答_开发者

JavaScript "Uncaught TypeError: object is not a function" associativity question

开发者 https://www.devze.com 2023-01-21 21:26 出处：网络

The code is as follows: <body> <a href="javascript:;" id="test">hello</a>

相关专题：javascript

The code is as follows:

<body>
    <a href="javascript:;" id="test">hello</a>
</body>

<script type="text/javascript">
    document.getElementById("test").addEventListener("click", function () {
      test()
    }, false)
    function test() {
      var postTypes = new Array('hello', 'there')
      (function() { alert('hello there') })()
    }
</script>

This will throw an:

"Uncaught TypeError: object is not a function"

If I wrap the anonymous function call/invocation in another set of parentheses it will execute the alert, but still give me an error. If I put a semicolon after the "var postTypes" definition then it will be completely fine.

I was led to believe that JavaScript does not require semicolon开发者_如何转开发s, so I'm making a guess that there is some weird associativity rules of function application that I am not fully understanding. Why am I getting this error?

JavaScript does require semicolons. It's just that the interpreter will insert them for you on line breaks where possible^*.

Unfortunately, the code

var a = new B(args)(stuff)()

does not result in a syntax error, so no ; will be inserted. (An example which can run is

var answer = new Function("x", "return x")(function(){return 42;})();

To avoid surprises like this, train yourself to always end a statement with ;.

^* This is just a rule of thumb and not always true. The insertion rule is much more complicated. This blog page about semicolon insertion has more detail.

Your code experiences a case where the automatic semicolon insertion (ASI) process doesn't happen.

You should never rely on ASI. You should use semicolons to properly separate statements:

var postTypes = new Array('hello', 'there'); // <--- Place a semicolon here!!

(function() { alert('hello there') })();

Your code was actually trying to invoke the array object.

I ran into this problem in React: I tried to destructure and use a named export when it was a default export, for example:

// module.js
const myFunction = () => null
export default myFunction

// component.js
// THIS WAS WRONG:
// import { myFunction } from './module'
// SHOULD BE THIS:
import myFunction from './module'

I got a similar error and it took me a while to realize that in my case I named the array variable payInvoices and the function also payInvoices. It confused AngularJS.

Once I changed the name to processPayments() it finally worked.

Try to have the function body before the function call in your JavaScript file.

I was getting this same error and spent a day and a half trying to find a solution. Naomi's answer lead me to the solution I needed.

My input (type=button) had an attribute name that was identical to a function name that was being called by the onClick event. Once I changed the attribute name, everything worked.

<input type="button" name="clearEmployer" onClick="clearEmployer();">

changed to:

<input type="button" name="clearEmployerBtn" onClick="clearEmployer();">

I have this error when compiling and bundling TypeScript code with Webpack. It compiles export class AppRouterElement extends connect(store, LitElement){....} into let Sr = class extends (Object(wr.connect) (fn, vr)) {....} which seems wrong because of the missing comma. When bundling with Rollup, no error.