Read File Inputs from Go WASM (used in https://donatstudios.com/Read-User-Files-With-Go-WASM)

example.go

package main

import (
	"syscall/js"
)

func main() {
	quit := make(chan struct{}, 0)

	document := js.Global().Get("document")
	document.Get("body").Call("insertAdjacentHTML", "beforeend", `
		<input type="file" id="fileInput">
		<output id="fileOutput"></output>
	`)

	fileInput := document.Call("getElementById", "fileInput")
	fileOutput := document.Call("getElementById", "fileOutput")

	fileInput.Set("oninput", js.FuncOf(func(v js.Value, x []js.Value) any {
		fileInput.Get("files").Call("item", 0).Call("arrayBuffer").Call("then", js.FuncOf(func(v js.Value, x []js.Value) any {
			data := js.Global().Get("Uint8Array").New(x[0])
			dst := make([]byte, data.Get("length").Int())
			js.CopyBytesToGo(dst, data)
			
			out := string(dst)
			if len(out) > 100 {
				out = out[:100] + "..."
			}


			fileOutput.Set("innerText", out)

			return nil
		}))

		return nil
	}))

	<-quit
}

Isn’t this just reading the first part of the file, when the file is bigger than Uint8Array?

@elgohr

if len(out) > 100 {
	out = out[:100] + "..."
}

This part is limiting it to the first hundred bytes for demonstrative purposes, but the Uint8Array can hold an arbitrary amount of data.