eslint/docs/rules/max-nested-callbacks.md

   1 # enforce a maximum depth that callbacks can be nested (max-nested-callbacks)
   2
   3 Many JavaScript libraries use the callback pattern to manage asynchronous operations. A program of any complexity will most likely need to manage several asynchronous operations at various levels of concurrency. A common pitfall that is easy to fall into is nesting callbacks, which makes code more difficult to read the deeper the callbacks are nested.
   4
   5 ```js
   6 foo(function () {
   7     bar(function () {
   8         baz(function() {
   9             qux(function () {
  10
  11             });
  12         });
  13     });
  14 });
  15 ```
  16
  17 ## Rule Details
  18
  19 This rule enforces a maximum depth that callbacks can be nested to increase code clarity.
  20
  21 ## Options
  22
  23 This rule has a number or object option:
  24
  25 * `"max"` (default `10`) enforces a maximum depth that callbacks can be nested
  26
  27 **Deprecated:** The object property `maximum` is deprecated; please use the object property `max` instead.
  28
  29 ### max
  30
  31 Examples of **incorrect** code for this rule with the `{ "max": 3 }` option:
  32
  33 ```js
  34 /*eslint max-nested-callbacks: ["error", 3]*/
  35
  36 foo1(function() {
  37     foo2(function() {
  38         foo3(function() {
  39             foo4(function() {
  40                 // Do something
  41             });
  42         });
  43     });
  44 });
  45 ```
  46
  47 Examples of **correct** code for this rule with the `{ "max": 3 }` option:
  48
  49 ```js
  50 /*eslint max-nested-callbacks: ["error", 3]*/
  51
  52 foo1(handleFoo1);
  53
  54 function handleFoo1() {
  55     foo2(handleFoo2);
  56 }
  57
  58 function handleFoo2() {
  59     foo3(handleFoo3);
  60 }
  61
  62 function handleFoo3() {
  63     foo4(handleFoo4);
  64 }
  65
  66 function handleFoo4() {
  67     foo5();
  68 }
  69 ```
  70
  71 ## Further Reading
  72
  73 * [Control flow in Node.js](http://book.mixu.net/node/ch7.html)
  74 * [Control Flow in Node](https://howtonode.org/control-flow)
  75 * [Control Flow in Node Part II](https://howtonode.org/control-flow-part-ii)
  76
  77 ## Related Rules
  78
  79 * [complexity](complexity.md)
  80 * [max-depth](max-depth.md)
  81 * [max-len](max-len.md)
  82 * [max-lines](max-lines.md)
  83 * [max-lines-per-function](max-lines-per-function.md)
  84 * [max-params](max-params.md)
  85 * [max-statements](max-statements.md)