projects / pve-eslint.git / blame
| Commit | Line | Data |
|---|---|---|
| eb39fafa DC |
1 | # Disallow unnecessary `.call()` and `.apply()`. (no-useless-call) |
| 2 | ||
| 3 | The function invocation can be written by `Function.prototype.call()` and `Function.prototype.apply()`. | |
| 4 | But `Function.prototype.call()` and `Function.prototype.apply()` are slower than the normal function invocation. | |
| 5 | ||
| 6 | ## Rule Details | |
| 7 | ||
| 8 | This rule is aimed to flag usage of `Function.prototype.call()` and `Function.prototype.apply()` that can be replaced with the normal function invocation. | |
| 9 | ||
| 10 | Examples of **incorrect** code for this rule: | |
| 11 | ||
| 12 | ```js | |
| 13 | /*eslint no-useless-call: "error"*/ | |
| 14 | ||
| 15 | // These are same as `foo(1, 2, 3);` | |
| 16 | foo.call(undefined, 1, 2, 3); | |
| 17 | foo.apply(undefined, [1, 2, 3]); | |
| 18 | foo.call(null, 1, 2, 3); | |
| 19 | foo.apply(null, [1, 2, 3]); | |
| 20 | ||
| 21 | // These are same as `obj.foo(1, 2, 3);` | |
| 22 | obj.foo.call(obj, 1, 2, 3); | |
| 23 | obj.foo.apply(obj, [1, 2, 3]); | |
| 24 | ``` | |
| 25 | ||
| 26 | Examples of **correct** code for this rule: | |
| 27 | ||
| 28 | ```js | |
| 29 | /*eslint no-useless-call: "error"*/ | |
| 30 | ||
| 31 | // The `this` binding is different. | |
| 32 | foo.call(obj, 1, 2, 3); | |
| 33 | foo.apply(obj, [1, 2, 3]); | |
| 34 | obj.foo.call(null, 1, 2, 3); | |
| 35 | obj.foo.apply(null, [1, 2, 3]); | |
| 36 | obj.foo.call(otherObj, 1, 2, 3); | |
| 37 | obj.foo.apply(otherObj, [1, 2, 3]); | |
| 38 | ||
| 39 | // The argument list is variadic. | |
| 40 | // Those are warned by the `prefer-spread` rule. | |
| 41 | foo.apply(undefined, args); | |
| 42 | foo.apply(null, args); | |
| 43 | obj.foo.apply(obj, args); | |
| 44 | ``` | |
| 45 | ||
| 46 | ## Known Limitations | |
| 47 | ||
| 48 | This rule compares code statically to check whether or not `thisArg` is changed. | |
| 49 | So if the code about `thisArg` is a dynamic expression, this rule cannot judge correctly. | |
| 50 | ||
| 51 | Examples of **incorrect** code for this rule: | |
| 52 | ||
| 53 | ```js | |
| 54 | /*eslint no-useless-call: "error"*/ | |
| 55 | ||
| 56 | a[i++].foo.call(a[i++], 1, 2, 3); | |
| 57 | ``` | |
| 58 | ||
| 59 | Examples of **correct** code for this rule: | |
| 60 | ||
| 61 | ```js | |
| 62 | /*eslint no-useless-call: "error"*/ | |
| 63 | ||
| 64 | a[++i].foo.call(a[i], 1, 2, 3); | |
| 65 | ``` | |
| 66 | ||
| 67 | ## When Not To Use It | |
| 68 | ||
| 69 | If you don't want to be notified about unnecessary `.call()` and `.apply()`, you can safely disable this rule. | |
| 70 | ||
| 71 | ## Related Rules | |
| 72 | ||
| 73 | * [prefer-spread](prefer-spread.md) |