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Creating read-only JS object
// lo-dash lib is the dependency
function readOnly(target){
var _readOnly = function (target, acc) {
// acc is passed into the function to be used for observer
var _defineProperty = function (propName, target, acc) {
var i, len;
// operation to be performed when add occurred
var addOp = function (cArg) {
// have to define the added item
_defineProperty(cArg.name, cArg.object, acc[propName]);
};
// operation to be performed when add delete
var delOp = function (cArg) {
if (_.isPlainObject(cArg.object)) {
delete acc[propName][cArg.name];
}
if (_.isArray(cArg.object)) {
// this fixes the array
acc[propName].unshift(acc[propName].shift());
// when splice occures, there's no
// clear indication what has been removed
// so, we need to find the diff, and clear acc
var args = _.difference(acc[propName], cArg.object);
args.unshift(acc[propName]);
_.pull.apply(null, args);
}
};
// function that is called when any change in the property happens
var observeFn = function (changes) {
for (i = 0, len = changes.length; i < len; i += 1) {
switch(changes[i].type) {
case 'new':
addOp(changes[i]);
break;
case 'deleted':
delOp(changes[i]);
break;
default:
continue;
}
}
};
if (_.isArray(target[propName])) {
Object.defineProperty(acc, propName, {
configurable: true,
enumerable: true,
value: []
});
Object.observe(target[propName], observeFn);
_readOnly(target[propName], acc[propName]);
}
else if (_.isPlainObject(target[propName])) {
Object.defineProperty(acc, propName, {
configurable: true,
enumerable: true,
value: {}
});
Object.observe(target[propName], observeFn);
_readOnly(target[propName], acc[propName]);
}
// value is the primitive one
else {
Object.defineProperty(acc, propName, {
configurable: true,
enumerable: true,
get: function () {
return target[propName];
}
});
}
};
// target is an array
_.forEach(target, function (val, key) {
_defineProperty(key, target, acc);
});
return acc;
};
if (Array.isArray(target)) {
return _readOnly(target, []);
}
else {
return _readOnly(target, {});
}
}
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