expression : word to find

// Word to be styled
target = "test";

// Original text from the layer
t = text.sourceText;

// Build a regex to find the target word (case‑insensitive)
// \b ensures we match whole words only
regex = new RegExp("\\b" + target + "\\b", "i");

// Try to find the word in the text
match = t.match(regex);

if (!match) {
    // If the word is not found, return the text unchanged
    t;
} else {
    // Character index where the matched word starts
    start = match.index;

    // Character index where the matched word ends
    end = start + match[0].length;

    // Split the text into three parts:
    // before the word, the word itself, and after the word
    before = t.slice(0, start);
    word = t.slice(start, end);
    after = t.slice(end);

    // Rebuild the full string (not strictly necessary here,
    // but useful if you later modify the structure)
    s = before + word + after;

    // Apply the font only to the character range of the matched word
    t.style.setFont("MyriadPro-Regular", start, end - start);
}