How to read cesium.js source code correctly?

For example, when I want to view the source code of Cesium3DTileContent.featuresLength or getFeature(), I can only see the following.

Object.defineProperties(Cesium3DTileContent.prototype, {
    featuresLength: {
        get: function () {

Cesium3DTileContent.prototype.getFeature = function (batchId) {

Where is the real code?

I already know that there are a lot of virtual base classes in cesium.js.
Cesium3DTileContent is one of them.

What i need to check is…
Batched3DModel3DTileContent.js, Geometry3DTileContent.js, Instanced3DModel3DTileContent.js…


Great question. It is important to be able to look through the source code. What file are you looking at in particular? It seems like you have found the header of the function. If you scroll down (or use command + f) you should be able to find more information on featuresLength or getFeature().