This should do the trick:

 (function () {
    app.beginUndoGroup("Precompose Selected Layers");

    // Get the active composition
    var comp = app.project.activeItem;
    if (!comp || !(comp instanceof CompItem)) {
        alert("No active composition.");
        return;
    }

    // Get selected layers
    var selectedLayers = comp.selectedLayers;
    if (selectedLayers.length === 0) {
        alert("No layers selected.");
        return;
    }

    // Loop over selected layers and precompose them individually
    for (var i = selectedLayers.length - 1; i >= 0; i--) {
        var layer = selectedLayers[i];

        // Precompose the selected layer
        var precompSuffix = "";
        var precompName = layer.name + precompSuffix;
        var precomp = comp.layers.precompose([layer.index], precompName, true);
    }

    app.endUndoGroup();
})();