55 lines
1.1 KiB
JavaScript
55 lines
1.1 KiB
JavaScript
export function computed(fn, dependencies = []) {
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const subscribers = new Set();
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const dependents = new Set();
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let isDirty = true;
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let val;
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function _computedDirtyReporter(_, skipPropagation) {
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if (!isDirty) {
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isDirty = true;
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dependents.forEach(d => d(_, skipPropagation));
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}
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if (subscribers.size && !skipPropagation) {
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accessor();
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}
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}
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const dependentSubscriptions = Array.from(dependencies).map(d => d._d(_computedDirtyReporter));
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const accessor = function _computed() {
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if (isDirty) {
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const newVal = fn.apply(null, dependencies.map(runParam));
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isDirty = false;
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if (newVal !== val) {
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val = newVal;
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subscribers.forEach(s => s(val));
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}
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}
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return val;
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};
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accessor.subscribe = fn => {
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subscribers.add(fn);
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return () => {
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subscribers.delete(fn);
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return subscribers.size;
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};
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};
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accessor._d = fn => {
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dependents.add(fn);
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return () => dependents.delete(fn);
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};
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accessor.detach = () => {
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subscribers.clear();
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dependents.clear();
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dependentSubscriptions.forEach(runParam);
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};
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return accessor;
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}
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const runParam = a => a();
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