javascript object item name

Question

I have following javascript code:

var oReg = new Object;
oReg.a = {size: 762, content: 0};
oReg.b = {size: 342, content: 0};
//...

for (var s in oReg) {
    oReg[s].set = function(i) {
        alert('#name of oReg item#: ' + i);
    }
}

Where is "#name of oReg item#" should be a, b etc
I think it should be begin with this, but I cant make it out.

instead of "#name of oReg item#" should be "s", but you cant write "s" because the variable does not exists in the function itself, only in the loop — andrew, Mar 31 '13 at 22:37
@andrew The variable does exist outside the loop, but it will always point to the last key when `set` is invoked. — bfavaretto, Mar 31 '13 at 22:38

score 3 · Accepted Answer · edited May 23 '17 at 10:25

It should be s instead of i, but unfortunately it isn't that simple because of the "infamous loop problem". You have to create a new scope on each iteration (functions create scopes), to be able to keep a reference to each value of s. Otherwise, your setter will always return the value of the last object key.

The following code should do it:

for (var s in oReg) {
    oReg[s].set = (function(key) {
        return function() {
            alert('#name of oReg item#: ' + key);
        }
    }(s));
}

score 0 · Answer 2 · answered Mar 31 '13 at 22:40

0

I know lots of people will start to cry seeing a call to eval in code, but that's really only dangerous when throwing user input into it. Therefore:

var oReg = new Object;
oReg.a = {size: 762, content: 0};
oReg.b = {size: 342, content: 0};

for (var s in oReg) {
    eval("oReg[s].set = function(i){alert('oReg."+s+": ' + i);}");
}

answered Mar 31 '13 at 22:40

tomsmeding

916
7
25

1

*"that's really only dangerous when throwing user input into it"*... you are right, but there are other reasons for avoiding `eval`: it's slow, more difficult for the compiler to optimize and the code is harder to maintain. – Felix Kling Mar 31 '13 at 22:52
Comments accepted, I guess I learned something today again :) Take bfavaretto's answer instead. – tomsmeding Mar 31 '13 at 22:55

score 0 · Answer 3 · answered Mar 31 '13 at 22:42

0

var oReg = new Object;
oReg.a = {size: 762, content: 0};
oReg.b = {size: 342, content: 0};
//...

for (var s in oReg) {
    oReg[s].set = (function(s) {
        alert('#name of oReg item#: ' + s);
    })(s);
}

I think you trying do this.

answered Mar 31 '13 at 22:42

Ilia Sidorenko

2,157
3
26
30

This will alert on each iteration, and `set` will be undefined for every key. – bfavaretto Mar 31 '13 at 22:59

javascript object item name

3 Answers3