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svelte/store.js

89 lines
1.6 KiB

import { run_all } from './internal.js';
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export function readable(start, value) {
const subscribers = [];
let stop;
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function set(newValue) {
if (newValue === value) return;
value = newValue;
subscribers.forEach(fn => fn(value));
}
return {
subscribe(fn) {
if (subscribers.length === 0) {
stop = start(set);
}
subscribers.push(fn);
fn(value);
return function() {
const index = subscribers.indexOf(fn);
if (index !== -1) subscribers.splice(index, 1);
if (subscribers.length === 0) {
stop && stop();
stop = null;
}
};
}
};
}
export function writable(value) {
const subscribers = [];
function set(newValue) {
if (newValue === value) return;
value = newValue;
subscribers.forEach(fn => fn(value));
}
function update(fn) {
set(fn(value));
}
function subscribe(fn) {
subscribers.push(fn);
fn(value);
return () => {
const index = subscribers.indexOf(fn);
if (index !== -1) subscribers.splice(index, 1);
};
}
return { set, update, subscribe };
}
export function derive(stores, fn) {
const single = !Array.isArray(stores);
if (single) stores = [stores];
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const auto = fn.length === 1;
return readable(set => {
let inited = false;
const values = [];
const sync = () => {
const result = fn(single ? values[0] : values, set);
if (auto) set(result);
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}
const unsubscribers = stores.map((store, i) => store.subscribe(value => {
values[i] = value;
if (inited) sync();
}));
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inited = true;
sync();
return function stop() {
run_all(unsubscribers);
};
});
}