Loading .js file in <head>
Question
So I am new to javascript (in fact, new to programming in general).
My question is, can I consider loading the .js file in the
<head><script src="script.js"></script>...</head>
as loading a header file (like in c/c++)?
I guess not. Suppose my script.js looks like this:
function copyToClipboard(text)
{window.prompt("Copy to clipboard: Ctrl+C, Enter", text);}
and my index.html looks like this:
<!DOCTYPE html>
<html>
<head>
<script src="script.js"></script>
</head>
<body>
<textarea id="a" autofocus="true"></textarea>
<script> onclick=copyToClipboard(document.getElementById("a").value);
</script>
</body>
</html>
It does not work, namely, it does not wait for my clicking (which means that the function is loaded correctly-it is called successfully, it is just that the pop-up does not wait for the mouse event). But if I put the script in-line, it works:
<!DOCTYPE html>
<html>
<head>
</head>
<body>
<textarea id="a" autofocus="true"></textarea>
<script>onclick=function copyToClipboard(text) {
window.prompt("Copy to clipboard:Ctrl+C,Enter",document.getElementById("a").value);
}
</script>
</body>
</html>
2 answers
solution1
3 ACCPTED 2014-06-01 07:01:34
The reason why the first code doesn't work is that you're calling the copyToClipboard() function and assigning the return value to the onclick variable. In the second code you're correctly assigning it a function reference instead of calling the function immediately.
In other words:
onclick = copyToClipboard(document.getElementById("a").value);
"Call copyToClipboard() , assign return value ( undefined ) to the onclick variable"
onclick = function copyToClipboard(text) { ...
"Assign a reference to a function called copyToClipboard() to the onclick variable"
To make it work with the function definition in an external script, wrap the function call in an anonymous function:
onclick = function() {
copyToClipboard(document.getElementById("a").value);
};
solution2
3 2014-06-01 07:05:33
All praise the power of javascript to mislead developers into diagnosing their problems incorrectly!
This is not how you define an inline onclick handler. An inline onclick handler is an attribute(or property, as we'll find out in a bit) of an html element:
<textarea id="a" autofocus="true" onclick="copyToClipboard(this.textContent)"></textarea>
What you did with the <script> tag was simply include some javascript code, to be executed as the browser is parsing your html:
<script> onclick=copyToClipboard(document.getElementById("a").value);</script> calls your function, and assigns its return value to onclick .
But wait, why does your second snippet work?
This is because onclick is also a property of dom elements. It also happens that you can assign a click handler to window itself - this is what your second snippet is actually doing(thanks to an uncool feature of javascript that attempts to assign to an undefined variable assigns to properties of the global object). That means that no matter where you click, your new click handler will be called.
As to your opening question, you can't really say that tags are like includes - a script can involve more than just declarations and definitions, unlike an included file. You can look into some of the module standards/frameworks, like RequireJS , for more similar functionality.
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