javascript custom object defineproperty code example
Example 1: js defineProperty
var o = {}; // Creates a new object
// Example of an object property added
// with defineProperty with a data property descriptor
Object.defineProperty(o, 'a', {
value: 37,
writable: true,
enumerable: true,
configurable: true
});
// 'a' property exists in the o object and its value is 37
// Example of an object property added
// with defineProperty with an accessor property descriptor
var bValue = 38;
Object.defineProperty(o, 'b', {
// Using shorthand method names (ES2015 feature).
// This is equivalent to:
// get: function() { return bValue; },
// set: function(newValue) { bValue = newValue; },
get() { return bValue; },
set(newValue) { bValue = newValue; },
enumerable: true,
configurable: true
});
o.b; // 38
// 'b' property exists in the o object and its value is 38
// The value of o.b is now always identical to bValue,
// unless o.b is redefined
// You cannot try to mix both:
Object.defineProperty(o, 'conflict', {
value: 0x9f91102,
get() { return 0xdeadbeef; }
});
// throws a TypeError: value appears
// only in data descriptors,
// get appears only in accessor descriptors
Example 2: js defineProperty
// using __proto__
var obj = {};
var descriptor = Object.create(null); // no inherited properties
descriptor.value = 'static';
// not enumerable, not configurable, not writable as defaults
Object.defineProperty(obj, 'key', descriptor);
// being explicit
Object.defineProperty(obj, 'key', {
enumerable: false,
configurable: false,
writable: false,
value: 'static'
});
// recycling same object
function withValue(value) {
var d = withValue.d || (
withValue.d = {
enumerable: false,
writable: false,
configurable: false,
value: value
}
);
// avoiding duplicate operation for assigning value
if (d.value !== value) d.value = value;
return d;
}
// ... and ...
Object.defineProperty(obj, 'key', withValue('static'));
// if freeze is available, prevents adding or
// removing the object prototype properties
// (value, get, set, enumerable, writable, configurable)
(Object.freeze || Object)(Object.prototype);