eslint/docs/rules/no-catch-shadow.md

   1 # Disallow Shadowing of Variables Inside of catch (no-catch-shadow)
   2
   3 This rule was **deprecated** in ESLint v5.1.0.
   4
   5 In IE 8 and earlier, the catch clause parameter can overwrite the value of a variable in the outer scope, if that variable has the same name as the catch clause parameter.
   6
   7 ```js
   8 var err = "x";
   9
  10 try {
  11     throw "problem";
  12 } catch (err) {
  13
  14 }
  15
  16 console.log(err)    // err is 'problem', not 'x'
  17 ```
  18
  19 ## Rule Details
  20
  21 This rule is aimed at preventing unexpected behavior in your program that may arise from a bug in IE 8 and earlier, in which the catch clause parameter can leak into outer scopes. This rule will warn whenever it encounters a catch clause parameter that has the same name as a variable in an outer scope.
  22
  23 Examples of **incorrect** code for this rule:
  24
  25 ```js
  26 /*eslint no-catch-shadow: "error"*/
  27
  28 var err = "x";
  29
  30 try {
  31     throw "problem";
  32 } catch (err) {
  33
  34 }
  35
  36 function err() {
  37     // ...
  38 };
  39
  40 try {
  41     throw "problem";
  42 } catch (err) {
  43
  44 }
  45 ```
  46
  47 Examples of **correct** code for this rule:
  48
  49 ```js
  50 /*eslint no-catch-shadow: "error"*/
  51
  52 var err = "x";
  53
  54 try {
  55     throw "problem";
  56 } catch (e) {
  57
  58 }
  59
  60 function err() {
  61     // ...
  62 };
  63
  64 try {
  65     throw "problem";
  66 } catch (e) {
  67
  68 }
  69 ```
  70
  71 ## When Not To Use It
  72
  73 If you do not need to support IE 8 and earlier, you should turn this rule off.