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One `observe` for all svelte needs.
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export function observe(key, callback, opts) { | |
const single = !Array.isArray(key); | |
const keypaths = single ? [ key ] : key; | |
const parts = keypaths.map(keypath => keypath.replace(/\[(\d+)\]/g, '.$1').split('.')); | |
const keys = parts.map(parts => parts[0]); | |
const fn = callback.bind(this); | |
let last = parts.map(parts => getNestedValue(this.get(), parts)); | |
if (!opts || opts.init !== false) { | |
single ? fn(last[0], undefined) : fn(last, last.map(_ => undefined)); | |
} | |
return this.on( | |
opts && opts.defer ? 'update' : 'state', | |
({ changed, current, previous }) => { | |
if (!previous) return; // prevent double-firing if observing in oncreate | |
let i = keys.length; | |
while (i--) { | |
if (changed[keys[i]]) { | |
let j = parts.length; | |
const values = parts.map(parts => getNestedValue(current, parts)); | |
if (!values.every((value, i) => value === last[i])) { | |
single ? fn(values[0], last[0]) : fn(values, last); | |
last = values; | |
} | |
return; | |
} | |
} | |
} | |
); | |
} | |
function getNestedValue(obj, parts) { | |
for (let i = 0; i < parts.length; i += 1) { | |
if (!obj) return undefined; | |
obj = obj[parts[i]]; | |
} | |
return obj; | |
} |
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