Created
May 12, 2019 19:07
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JavaScript snoop properties of objects. Bind callbacks to getters and setters for all properties of an object. Useful for observing how a page element has its properties accessed
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/** | |
* Snoops on an object, monitors all attempts to access and set properties | |
* @param {Object} obj - the object to monitor | |
* @param {string[]=} props - list of properties to watch, watches all properties by default | |
* @param {Function=} onset - callback when the property is set (newValue is passed) | |
* @param {Function=} onget - callback when the property is accessed | |
* @param verbose | |
*/ | |
function snoopProperty(obj, props = [], onset = (val) => null, onget = () => null, verbose = true) { | |
if (typeof onset !== 'function') onset = (val) => null; | |
if (typeof onget !== 'function') onget = () => null; | |
var snooper = { | |
object: obj, | |
props: props, | |
records: { | |
sets: [], | |
gets: [], | |
}, | |
/** | |
* @param props the properties to snoop | |
*/ | |
snoop: function (props) { | |
if (props.length === 0) { // default to all properties | |
props = Object.keys(obj); | |
} else if (!!props && !props.length) { | |
props = [props]; | |
} | |
for (const prop of props) { | |
obj['__' + prop] = obj[prop]; // actual property | |
snooper.object.__defineSetter__(prop, function (newValue) { | |
if(verbose) console.warn( | |
'Snooper: [', prop, '] was just changed from "', snooper.object['__' + prop], '" to -> "', newValue, '"', | |
'\non:', snooper.object | |
); | |
snooper.records.sets.push({timeStamp: Date.now(), from: snooper.object['__' + prop], to: newValue}); | |
onset.call(snooper.object, newValue); | |
snooper.object['__' + prop] = newValue; | |
}); | |
snooper.object.__defineGetter__(prop, function () { | |
if(verbose) console.warn( | |
'Snooper: [', prop, '] was just accessed "', snooper.object['__' + prop], '"', | |
'\non:', snooper.object | |
); | |
snooper.records.gets.push({timeStamp: Date.now(), value: snooper.object['__' + prop]}); | |
onget.call(snooper.object); | |
return snooper.object['__' + prop]; | |
}); | |
} | |
}, | |
abort: function (props) { | |
if (props.length === 0) { // default to all properties | |
props = Object.keys(obj); | |
} else if (!!props && !props.length) { | |
props = [props]; | |
} | |
for (const prop of props) { | |
snooper.object.__defineSetter__(prop, newValue => { | |
snooper.object['__' + prop] = newValue; | |
}); | |
snooper.object.__defineGetter__(prop, () => snooper.object['__' + prop]); | |
} | |
} | |
}; | |
snooper.snoop(props); | |
return snooper; | |
} |
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