use an if block, it's clearer

pull/13767/head
Rich Harris 2 years ago
parent 1e2afeffd0
commit f6163c113a

@ -125,11 +125,11 @@ An effect only reruns when the object it reads changes, not when a property insi
<p>{state.value} doubled is {derived.value}</p>
```
An effect only depends on the values that it read the last time it ran. This implementation detail has interesting implications for effects that have conditional short-circuiting code.
An effect only depends on the values that it read the last time it ran. This has interesting implications for effects that have conditional code.
For instance, if `a` is `false` in the code snippet below, the `a || b` operation will proceed to read `a` and _then_ `b`. This double read causes the effect to depend on both `a` and `b`, which in turn causes the effect to rerun whenever any of `a` or `b` change.
For instance, if `a` is `true` in the code snippet below, the code inside the `if` block will run and `b` will be evaluated. As such, changes to either `a` or `b` [will cause the effect to re-run](/#H4sIAAAAAAAAE3WQTWrDMBCFrzIRAcsQkr1rC3KIruouJHUURNWxscalRejuleqEQElXQu99b_6SIP2BohPPxJ4DvomDcD5gFN1LEvw9V68KRb-S53k-xk8MXDWjIz7S7USMxKWM6KNd_MxqpLE0YNAwwD6yZpROh4jt080xj5zi7dE5tCxlC4OCVKWRS4c4BTyG6SKbZSXydGm2WhvgHUjd3vA_AdM1BzBXnHN9cv31p_u01JuVeSKYyAZv34e0DVAX2OmsNPgISef-tHHq30RdbGeyMr8Jc0-USzF-seh4WTG_5h_LyPoejwEAAA==).
On the other hand, if `a` is `true`, changes to `b` will [not cause this effect to rerun](/#H4sIAAAAAAAAE3WQ0WrDMAxFf0U1hTow1vcsMfQ7lj3YjlxEXTvEymC4_vfFC6Ewtidxde8RkrJw5DGJ9j2LoO8oWnGZJvEi-GuqIn2iZ1x1istsa6dLdqaJ1RAG9sigoYdjYs0onfYJm7fdMX85q3dE59CylA30CnJtDWxjSNHjq49XeZqXEChcT9usLUAOpIbHA0yzM78oColGhDVofLS3neZSS6mqOz-XD51ZmGOAGKwne-vztk-956CL0kAJsi7decupf4l658EUZX4I8yTWt93jSI5wFC3PC5aP8g0Aje5DcQEAAA==) because the `a || b` operation _exits early_ as soon as it encounters the first truthy operand. By exiting early, the effect will have only read `a`, which causes the effect to _only_ depend on `a`, not `b`.
Conversely, if `a` is `false`, `b` will not be evaluated, and the effect will _only_ re-run when `a` changes.
```ts
let a = false;
@ -138,8 +138,8 @@ let b = false;
$effect(() => {
console.log('running');
if (a || b) {
console.log('inside if block');
if (a) {
console.log('b:', b);
}
});
```

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