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eb39fafa4f
includes a (minimal) working wrapper Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
74 lines
1.9 KiB
Markdown
74 lines
1.9 KiB
Markdown
# Disallow unnecessary `.call()` and `.apply()`. (no-useless-call)
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The function invocation can be written by `Function.prototype.call()` and `Function.prototype.apply()`.
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But `Function.prototype.call()` and `Function.prototype.apply()` are slower than the normal function invocation.
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## Rule Details
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This rule is aimed to flag usage of `Function.prototype.call()` and `Function.prototype.apply()` that can be replaced with the normal function invocation.
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Examples of **incorrect** code for this rule:
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```js
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/*eslint no-useless-call: "error"*/
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// These are same as `foo(1, 2, 3);`
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foo.call(undefined, 1, 2, 3);
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foo.apply(undefined, [1, 2, 3]);
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foo.call(null, 1, 2, 3);
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foo.apply(null, [1, 2, 3]);
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// These are same as `obj.foo(1, 2, 3);`
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obj.foo.call(obj, 1, 2, 3);
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obj.foo.apply(obj, [1, 2, 3]);
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```
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Examples of **correct** code for this rule:
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```js
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/*eslint no-useless-call: "error"*/
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// The `this` binding is different.
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foo.call(obj, 1, 2, 3);
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foo.apply(obj, [1, 2, 3]);
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obj.foo.call(null, 1, 2, 3);
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obj.foo.apply(null, [1, 2, 3]);
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obj.foo.call(otherObj, 1, 2, 3);
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obj.foo.apply(otherObj, [1, 2, 3]);
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// The argument list is variadic.
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// Those are warned by the `prefer-spread` rule.
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foo.apply(undefined, args);
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foo.apply(null, args);
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obj.foo.apply(obj, args);
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```
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## Known Limitations
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This rule compares code statically to check whether or not `thisArg` is changed.
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So if the code about `thisArg` is a dynamic expression, this rule cannot judge correctly.
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Examples of **incorrect** code for this rule:
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```js
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/*eslint no-useless-call: "error"*/
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a[i++].foo.call(a[i++], 1, 2, 3);
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```
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Examples of **correct** code for this rule:
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```js
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/*eslint no-useless-call: "error"*/
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a[++i].foo.call(a[i], 1, 2, 3);
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```
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## When Not To Use It
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If you don't want to be notified about unnecessary `.call()` and `.apply()`, you can safely disable this rule.
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## Related Rules
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* [prefer-spread](prefer-spread.md)
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