DEV Community

7 interesting deprecated JavaScript features

Nikola Stojaković on August 04, 2021

Since it’s birth 26 years ago at Netscape, JavaScript has come a long way. A language which was used only to interact with Java applets and do simp...

Read full post

Nguyen Tran Chau Giang • Aug 5 '21 • Edited

Some example with with

with(Math){max(1,2)}

To watch Object change, you can also Object.defineProperty

var o = {};
var bValue = 38;
Object.defineProperty(o, 'b', {,
  get() { console.log("Inside Get"); return bValue; },
  set(newValue) { console.log("Inside Set"); bValue = newValue; },
  enumerable: true,
  configurable: true
});
o.b=12
o.b

Mike Talbot ⭐ • Aug 4 '21

Great list, I didn't have a clue about some of those :)

One other way of doing a "with like thing" having a go at the C# syntax I've seen is this:


function scope(value, fn) {
    return fn(value)
}

const cat = {
    details: {
        passport: {
            location: {
                city: "New York"
            }
        }
    }
}

scope(cat.details.passport.location, _ => {
    _.city = "Meowyork"
})

Nikola Stojaković • Aug 4 '21

That's nice!

Nikola Stojaković • Aug 4 '21 • Edited

Yup, that's another way of doing it - although that will return

Uncaught SyntaxError: redeclaration of non-configurable global property location

in the browser since location is a global property - we can rename it to something else though.

lionel-rowe • Aug 4 '21 • Edited

Don't forget let and const are already block scoped, so a simple alternative to your let block example is this:

let catName = 'Oswald'
let catAge = 2.5

{
    let catName = 'Luna', catAge = 2
    console.log(`${catName} (${catAge} years old)`) // Luna (2 years old)
}

console.log(`${catName} (${catAge} years old)`) // Oswald (2.5 years old)

Nikola Stojaković • Aug 4 '21

You're right, thanks - I'll update the article now.

Kingkor Roy Tirtho • Aug 5 '21

I've to say JavaScript changed so much that its hard to keep track of what have changes... But Proxy thing is just blew my mind. I never knew it was available. Thanks a lot