HTTP & Files

Fetch makes HTTP requests straight from your WASM component. GetFileBytes reads a file the user picked. TriggerDownload pushes a file back to the browser.

Important: You must dot-import core/wasm (import . "github.com/gothicframework/core/wasm") for use these helpers, otherwise you will get a tinygo compile error.

Note: these calls are blocking. Go's goroutine model handles concurrency for you, so always call them inside a goroutine or a CreateWasmFunc handler.

// Inside CreateWasmFunc — already runs in its own goroutine
CreateWasmFunc("load", func() {
	body, err := Fetch("https://api.example.com/data")
	if err == nil { SetText("result", body) }
})

// On mount — use go keyword to avoid blocking the main WASM thread
go func() {
	body, err := Fetch("https://api.example.com/data")
	if err == nil { SetText("result", body) }
}()

CreateWasmFunc("load", func() {
	body, err := Fetch("https://api.example.com/todos/1")
	if err != nil {
		SetText("result", "error: "+err.Error())
		return
	}
	SetText("result", body)
})

Need more control? Pass a FetchConfig to set method, headers, body, or query parameters.

CreateWasmFunc("submit", func() {
	body, err := Fetch("https://api.example.com/todos", FetchConfig{
		Method:  "POST",
		Headers: map[string]string{"Content-Type": "application/json"},
		Body:    `{\"title\":\"buy milk\"}`,
	})
	if err != nil { return }
	SetText("result", body)
})

To handle uploads, read the user's selected file with GetFileBytes and send the []byte through BodyBytes.

CreateWasmFunc("uploadFile", func() {
	data := GetFileBytes("upload")
	if data == nil {
		SetText("status", "no file selected")
		return
	}
	_, err := Fetch("/api/upload", FetchConfig{
		Method:    "POST",
		Headers:   map[string]string{"Content-Type": "application/octet-stream"},
		BodyBytes: data,
	})
	if err != nil {
		SetText("status", "upload failed")
		return
	}
	SetText("status", "uploaded!")
})

Going the other way? FetchBytes downloads binary data, and TriggerDownload hands it to the user's browser as a file.

CreateWasmFunc("downloadReport", func() {
	data, err := FetchBytes("/api/report.csv")
	if err != nil { return }
	TriggerDownload("report.csv", data, "text/csv")
})

Need multiple WASM components to share state and react to each other? Check out Topics next!