Based on Petr's comment, it seems like the function is typically generated with such a code:
window["webpackJsonp"] = function webpackJsonpCallback(chunkIds, moreModules, executeModules) { // add "moreModules" to the modules object, // then flag all "chunkIds" as loaded and fire callback var moduleId, chunkId, i = 0, resolves = [], result; for(;i < chunkIds.length; i++) { chunkId = chunkIds[i]; if(installedChunks[chunkId]) { resolves.push(installedChunks[chunkId][0]); } installedChunks[chunkId] = 0; } for(moduleId in moreModules) { if(Object.prototype.hasOwnProperty.call(moreModules, moduleId)) { modules[moduleId] = moreModules[moduleId]; } } if(parentJsonpFunction) parentJsonpFunction(chunkIds, moreModules, executeModules); while(resolves.length) { resolves.shift()(); } if(executeModules) { for(i=0; i < executeModules.length; i++) { result = __webpack_require__(__webpack_require__.s = executeModules[i]); } } return result; };
The 3 parameter names and the comments on the source code are quite insightful.