What's wrong with my javascript?

Noah_S
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What's wrong with my javascript?

« on: a Summer day »

I'm trying to figure out some javascript in the w3school experiment box. So far I have

Code

<!DOCTYPE html>
<html>
<body>

<h2>Get the current URL</h2><span id="demo"></span>

<script>
if (window.location.href == https://www.w3schools.com/howto/tryit.asp?filename=tryhow_js_get_url) {
let text = "Yes";
} else {
let text = "No";
}

document.getElementById("demo").innerHTML = text;
</script>

</body>
</html>

It's not displaying anything when I run it. I can't figure out what's wrong. I've been trying different combinations, checking my ";"s, everything I can think of. The code doesn't even look complicated, but javascript is my weakest language and I can't figure out why this code refuses to cooperate.


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Dan Q
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Re: What's wrong with my javascript?

« Reply #1 on: a Summer day »

Looks like a syntax error to me. https://www.w3schools.com/howto/tryit.asp?filename=tryhow_js_get_url is a string, so it should be wrapped in some variety of quotation marks.

Without the quotation marks, it looks like you're asking whether window.location.href == https:. And then the // starts a comment. This is why - if you open your browser's debug tools - you'll see a syntax error complaining about a missing ) - you've commented out the end of the line which includes it!

Once you fix that, the next problem is that you're declaring (let) your variable inside a block ({ ... }). Which means that it won't exist outside that block.

Once you've fixed both of those problems, you get this, which seems to work:

Code

<!DOCTYPE html>
<html>
<body>

<h2>Get the current URL</h2><span id="demo"></span>
 
<script>
let text; // declare the variable here!
if (window.location.href == 'https://www.w3schools.com/howto/tryit.asp?filename=tryhow_js_get_url') {
  text = "Yes";
} else {
  text = "No";
}

document.getElementById("demo").innerHTML = text;
</script>

</body>
</html>


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Noah_S
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Re: What's wrong with my javascript?

« Reply #2 on: a Summer day »

Thank you.

I'm so used to PHP variables existing.


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Dan Q
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Re: What's wrong with my javascript?

« Reply #3 on: a Summer day »

So:

Classic JavaScript variable use the var keyword. And they're globally scoped. But you shouldn't be using them, because... well... global-scoping introduces terrible ways to shoot yourself in the foot. Modern JavaScript uses let and const, which not only help by ensuring that it's clear whether a variable will ever change... they also help by limiting the scope of the variable to the function or block in which they're defined. Generally much-cleaner programming.

PHP also has variable scoping. A variable declared in an object or function isn't available to a different object or function unless you pass it as a parameter (preferred) or use the 'global' keyword to share it between them. Click run code to run this example; then change the 'global' line so that one of the top-level variables doesn't get included in the function and try again to see a "Warning: Undefined variable".

So yeah: both (modern) JS and (normal) PHP do variable scoping in a similar way. The big difference is that JS scopes to "function OR block", where as PHP scopes to "function". If you declare a variable inside a loop in PHP, it's available outside the loop; but in JS it isn't. But both are scoped to the functions that contain them. They're more-similar than you'd think!


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