未被捕获的ReferenceError：您好未定义

Question

Any idea why I have the error Uncaught ReferenceError: hello is not defined ?

function hello() {
    console.log('hello ()');
    setTimeout("hello ()", 1000);
}
setTimeout("hello()", 1000);​

Here is a jsfiddle : http://jsfiddle.net/s9vLk/

Answer 1

The JavaScript code in your demo runs within the 'load' event handler (the option "onLoad" is selected). Therefore, the function hello is not a global function. You have to set the option to "no wrap (body)" or "no wrap (head)". That way, your JavaScript code will be global code.

Live demo: http://jsfiddle.net/s9vLk/1/

Answer 2

The problem is that you are passing strings to setTimeout() which means code in the string will effectively be eval ed and thus isn't running in the scope you think it's running in and so the hello() function isn't found.

If you change the jsfiddle options on the left from "onload" to "no wrap" it works as is because then the function will be global rather than nested inside the onload handler, but a better option is to pass a function reference to setTimeout() :

function hello() {
    console.log('hello ()');
    setTimeout(hello, 1000);
}
setTimeout(hello, 1000);

(Note: no parentheses after hello .)

Answer 3

You have a space between hello and the () .

You really should't pass the arguments as a string to setTimeout .

Answer 4

You don't (and shouldn't) need to reference your function name as a string.

function hello() {
    console.log('hello');
    setTimeout(hello, 1000);
}
setTimeout(hello, 1000);

Or better yet

setInterval(function() {
    console.log('hello');
}, 1000);