CODEWITHSUNDEEP
javascript
Roy
Roy

Reputation: 751

prototype value does not update for every instance in js, why?

if I set a prototype value and make two instances

then update the prototype value in one instance

now other instance prototype value does not update, why?

code is 

var A = function() {

}
A.prototype.u = 2;

var a = new A();

var b = new A();

a.u = 4
alert(a.u) // 4
alert(b.u) // 2

it's so unreasonable, it's prototype value not this value. right?

Upvotes: 2

Views: 210

Answers (1)

Quentin
Quentin

Reputation: 943142

You aren't "updating the prototype value". You are writing the new value to the local object and not to the prototype chain. The local property masks the one higher up the chain.

alert(a.u); looks at a, finds a u and alerts it.

alert(b.u); looks at b, doesn't find a u, looks up the prototype chain, finds a u and alerts it.

Compare:

var A = function() {

}
A.prototype.u = 2;

var a = new A();

var b = new A();

a.u = 4;
A.prototype.u = 6;
alert(a.u);
alert(b.u);

Upvotes: 6

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