I was trying out this really simple example from the awesome "Professional JavaScript for Web Developers" book by Nicholas Zakas but I can't figure what I am doing wrong here. Must be something really simple that I missed but I'm stuck.
Here is the code:
'use strict';
var book = {};
Object.defineProperties(book, {
originYear: {
value: 2004,
writable: false
},
_year: {
value: 2004
},
edition: {
value: 1
},
year : {
get: function() {
return this._year;
},
set: function(newValue) {
if(newValue > this.originYear) {
this._year = newValue;
this.edition += newValue - this.originYear;
}
}
}
});
console.log(book.edition);
book.year = 2006;
console.log(book.edition);
The error I am getting on the Chrome console is:
Uncaught TypeError: Cannot assign to read only property '_year' of #main.js:31 Object.defineProperties.year.setmain.js:39 (anonymous function)
Can someone please explain where I have gone wrong?
Here is the fiddle
3 Answers
When you use Object.defineProperties, by default writable is set to false, so _year and edition are actually read only properties.
Explicitly set them to writable: true:
_year: {
value: 2004,
writable: true
},
edition: {
value: 1,
writable: true
},
Check out MDN for this method.
writable
trueif and only if the value associated with the property may be changed with an assignment operator.
Defaults tofalse.
If sometimes a link! will not work. so create a temporary object and take all values from the writable object then change the value and assign it to the writable object. it should perfectly.
var globalObject = {
name:"a",
age:20
}
function() {
let localObject = {
name:'a',
age:21
}
this.globalObject = localObject;
}
I tried changing year to a different term, and it worked.
public_methods : {
get: function() {
return this._year;
},
set: function(newValue) {
if(newValue > this.originYear) {
this._year = newValue;
this.edition += newValue - this.originYear;
}
}
}
