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