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eb39fafa4f
includes a (minimal) working wrapper Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
99 lines
2.4 KiB
Markdown
99 lines
2.4 KiB
Markdown
# Disallow Functions in Loops (no-loop-func)
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Writing functions within loops tends to result in errors due to the way the function creates a closure around the loop. For example:
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```js
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for (var i = 0; i < 10; i++) {
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funcs[i] = function() {
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return i;
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};
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}
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```
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In this case, you would expect each function created within the loop to return a different number. In reality, each function returns 10, because that was the last value of `i` in the scope.
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`let` or `const` mitigate this problem.
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```js
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/*eslint-env es6*/
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for (let i = 0; i < 10; i++) {
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funcs[i] = function() {
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return i;
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};
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}
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```
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In this case, each function created within the loop returns a different number as expected.
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## Rule Details
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This error is raised to highlight a piece of code that may not work as you expect it to and could also indicate a misunderstanding of how the language works. Your code may run without any problems if you do not fix this error, but in some situations it could behave unexpectedly.
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This rule disallows any function within a loop that contains unsafe references (e.g. to modified variables from the outer scope).
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Examples of **incorrect** code for this rule:
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```js
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/*eslint no-loop-func: "error"*/
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/*eslint-env es6*/
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for (var i=10; i; i--) {
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(function() { return i; })();
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}
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while(i) {
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var a = function() { return i; };
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a();
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}
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do {
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function a() { return i; };
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a();
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} while (i);
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let foo = 0;
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for (let i = 0; i < 10; ++i) {
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//Bad, `foo` is not in the loop-block's scope and `foo` is modified in/after the loop
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setTimeout(() => console.log(foo));
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foo += 1;
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}
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for (let i = 0; i < 10; ++i) {
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//Bad, `foo` is not in the loop-block's scope and `foo` is modified in/after the loop
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setTimeout(() => console.log(foo));
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}
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foo = 100;
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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-loop-func: "error"*/
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/*eslint-env es6*/
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var a = function() {};
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for (var i=10; i; i--) {
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a();
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}
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for (var i=10; i; i--) {
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var a = function() {}; // OK, no references to variables in the outer scopes.
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a();
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}
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for (let i=10; i; i--) {
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var a = function() { return i; }; // OK, all references are referring to block scoped variables in the loop.
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a();
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}
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var foo = 100;
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for (let i=10; i; i--) {
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var a = function() { return foo; }; // OK, all references are referring to never modified variables.
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a();
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}
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//... no modifications of foo after this loop ...
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```
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