Relative paths with fetch in Javascript
I was surprised by an experience with relative paths in Javascript today. I’ve boiled down the situation to the following:
Suppose you have a directory structure like:
app/
|
+--app.html
+--js/
|
+--app.js
+--data.json
All my app.html does is run js/app.js
<!DOCTYPE html>
<title>app.html</title>
<body>
<script src=js/app.js></script>
</body>
app.js loads the JSON file and sticks it at the beginning of body:
// js/app.js
fetch('js/data.json') // <-- this path surprises me
.then(response => response.json())
.then(data => app.data = data)
The data is valid JSON, just a string:
"Hello World"
This is a pretty minimal usage of fetch, but I am surprised that the URL that I pass to fetch has to be relative to app.html instead of relative to app.js. I would expect this path to work, since data.json and app.js are in the same directory (js/):
fetch('data.json') // nope
Is there an explanation for why this is the case?
Answer
When you say fetch('data.json') you are effectively requesting http://yourdomain.com/data.json since it is relative to the page your are making the request from. You should lead with forward slash, which will indicate that the path is relative to the domain root: fetch('/js/data.json'). Or fully quality with your domain fetch('http://yourdomain.com/js/data.json').