René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"util.debuglog callback argument behavior and purpose appears to be documented incorrectly","articleBody":"### Affected URL(s)\n\nhttps://nodejs.org/docs/latest/api/util.html#utildebuglogsection-callback\n\n### Description of the problem\n\nThe usage example of the callback function for `util.debuglog` is not sufficiently documented imho.\nMoreover, when looking at the code, it also seems to even work differently than described. \n\nThe example for the callback does the following:\n```javascript\nconst util = require('node:util');\nlet debuglog = util.debuglog('internals', (debug) =\u003e {\n  // Replace with a logging function that optimizes out\n  // testing if the section is enabled\n  debuglog = debug;\n});\n```\n\nWhat debuglog effectively does is:\n```javascript\nfunction debuglog(set, cb){\n  realLogFunction = (...args){\n     init() //sets up the set name and an enabled boolean value\n\n     // creates a noop function when enabled=false\n     realLogFunction = debugLogImpl(enabled) \n     if(typeof cb == \"function\"){\n       // this is the part where the documentation is lacking\n       cb(realLogFunction) //code depends on side-effects of the callback?\n     }\n     // this line is only effective the very first time, when still in the factory\n     // likely to not 'swallow' the first log line that lazily inits the real logger\n     realLogFunction(...args)\n  }\n\n  //left out for brewity, but works on the same principle as realLogFunction\n  let innerEnabledCheck ()=\u003e{...}\n  \n  logDelegate = (...) =\u003e {\n    //some switch on argument length, but effectively always results in the next line, with a varying\n    //amount of arguments passed on.\n    realLogFunction(args)\n  }\n  logDelegate.enabled = innerEnabledCheck() //left out for brewity\n  return logDelegate;\n}\n```\n\nThe first time `logDelegate` is called, the enabled test is already optimized out and `logDelegate` will call the now-changed `realLogFunction` generated from `debugLogImpl`.\nWhat actually happens when the callback is used as in the documentation's example, is that the outside variable, (`debuglog` in the example) which points to `logDelegate`, will be replaced by `realLogFunction`.\n\nThus, what is 'optimized out' is the switch in `logDelegate` when the callback is used as shown in the example, but at the price of also losing the `enabled` getter. 'Testing if the section is enabled' is always automatically and implicitly optimized out in the inner factory method.","author":{"url":"https://github.com/GB609","@type":"Person","name":"GB609"},"datePublished":"2025-01-21T10:41:14.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/56676/node/issues/56676"}