webR

How does the app work?

Look at the <script/> html section. R is started in a few key steps:

1. webR is imported, input and output html chunks are defined, and a new webR instance is made:

import { WebR } from "https://webr.r-wasm.org/latest/webr.mjs";

const statusEl = document.getElementById("status");
const outputEl = document.getElementById("output");
const runBtn = document.getElementById("run");

const webR = new WebR();

2. Default R code and data is created in in a webR.evalR() command. Note that await is used since this is an asynchronous operation.

await webR.evalR(`
    clean_seq <- function(x) {
        lines <- unlist(strsplit(x, "\\n"))
        seq_lines <- lines[!grepl("^>", lines)]
        seq <- paste(seq_lines, collapse = "")
        seq <- toupper(gsub("[^ACGT]", "", seq))
        seq
    } 
    ... `, { captureStreams: false });
}

How do data enter WASM here?

For the sequence input, they go into a html element defined as seq. These are then bound into R with webR.objs.globalEnv.bind()

runBtn.addEventListener("click", async () => {
runBtn.disabled = true;
statusEl.textContent = "Running...";

const seq = document.getElementById("seq").value;

// Move input text into R
await webR.objs.globalEnv.bind("rawseq", seq);

Input is then processed like above in webR.evalR()

const result = await webR.evalR(`
    library(stringr)

    seq_clean <- clean_seq(rawseq)
    gc <- gc_content(seq_clean)
    revseq <- rev_comp(seq_clean)

    paste(
        sprintf("Cleaned length: %d", gc$len),
        sprintf("GC bases: %d", gc$gc),
        sprintf("GC content: %.2f%%", gc$pct),
        "",
        "Reverse complement:",
        revseq,
        sep = "\\n"
    )
...)

How do data exist WASM?

R output is captured in the result variable defined above and then handed back to the DOM via :

const text = await result.toJs();
outputEl.textContent = text.values[0];
statusEl.textContent = "Done.";
runBtn.disabled = false;

Questions:

• What does captureStreams mean?
  When true, it captures R's console output (messages, warnings, prints). When false, it ignores console output and only returns the result value.

• What does result.toJS() do?
  Converts R objects from webR's internal format into JavaScript objects that can be used in JavaScript code. The result has a values array containing the actual data.

• What does runBtn.disabled = false mean?
  Re-enables the "Analyze sequence" button after processing is complete, allowing the user to click it again.