ArcGIS: Get layer by name using Javascript API and modify it

Question

I'm very new to ArcGIS and I'm developing a custom widget in the ArcGIS WebApp Builder that will allow me to change the style attribute of a specific layer in my map.

To manually change the style attribute I would open the map, hover over a layer and click 'Change style':

Then I would select the style attribute from the list that appears:

At the moment my JavaScript widget allows the user to pick from a list of (manually entered) layers and style attributes:

The function that is called when the user clicks 'Update' resembles the following:

_updateAttribute: function() {
    var lyr = document.getElementById("layer");
    var att = document.getElementById("attribute");
    var selectedLayer = lyr.options[lyr.selectedIndex].value;
    var selectedAttribute = att.options[att.selectedIndex].value;
    // Pseudo-code;
    // map.layer(selectedLayer).Attribute = selectedAttribute;
}

Is there a way to carry out the operation represented by my pseudo-code?

Answer 1

this sample actually shows what you want to do (click "Explore in the Sandbox" to see live demo)