load() fetch calls API twice if URL lacks trailing slash #14781

Describe the bug

i have an api running at http://localhost:8080 when i go to routes/+page.svelte and call load function from +page.ts

export async function load({ fetch }) {
    const data = await (await fetch("http://localhost:8080")).json()
    return {
        text: data.text
    }
}

it calls this api twice but when i put a trailing slash at end of url http://localhost:8080/ it calls the api once, after i debugged the code i found out that data serialized when load is called at server has selector data-sveltekit-fetched data-url="http://localhost:8080/" but in file kit/src/runtime/client/fetcher.js at line 158:

const url = JSON.stringify(resource instanceof Request ? resource.url : resource);

the resource is not constructed with new URL() so it doesn't add a trailing slash so this selector

let selector = `script[data-sveltekit-fetched][data-url=${url}]`;

doesnt get the serialized data and calls the api twice. so is this intentional or a mistake? changing the line 158 to this worked for me

const constructed_url = new URL(resource instanceof Request ? resource.url : resource).href
const url = JSON.stringify(constructed_url);

Reproduction

Create any +page.ts file and call any api

export async function load({ fetch }) {
    const data = await (await fetch("<api_url>")).json()
    return {
        text: data.text
    }
}

add trailing slash after <api_url>/ it calls the api one and remove / it calls this api twice

Logs

System Info

System:
    OS: Linux 6.16 Arch Linux
    CPU: (8) x64 Intel(R) Core(TM) i7-1065G7 CPU @ 1.30GHz
    Memory: 4.85 GB / 11.24 GB
    Container: Yes
    Shell: 5.9 - /usr/bin/zsh
  Binaries:
    Node: 24.8.0 - /usr/bin/node
    npm: 11.6.0 - /usr/bin/npm
    pnpm: 10.17.1 - /usr/bin/pnpm
    bun: 1.3.0 - /home/softrock/.bun/bin/bun
  Browsers:
    Brave Browser: 141.1.83.112
    Firefox: 143.0.1
    Firefox Developer Edition: 143.0.1

Severity

annoyance

Additional Information

No response