javascript - How to assign a value to a dynamic variable using eval? - Stack Overflow

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I got the dynamic variable name doing

varname = "data" + newid + "['" + name + "']";

I would like to assign a value to the dynamic variable. I tried this

eval(varname) = value; 

but it doesn't work. What do I need to do in order to assign a value to the dynamic variable?

I got the dynamic variable name doing

varname = "data" + newid + "['" + name + "']";

I would like to assign a value to the dynamic variable. I tried this

eval(varname) = value; 

but it doesn't work. What do I need to do in order to assign a value to the dynamic variable?

• javascript

Share Improve this question Follow edited Feb 24, 2016 at 18:35 Adam Michalik 9,9451313 gold badges7575 silver badges107107 bronze badges asked Sep 4, 2012 at 16:52 juria_robertsjuria_roberts 15511 gold badge22 silver badges1010 bronze badges 4

• 2 Don't use friggin' dynamic variables. Use objects. In particular, data[newid][name], and that works with assignment too. – user395760 Commented Sep 4, 2012 at 16:55
• actually I have inserted many jsons through php into my javascript with names in the format datafirst,datasecond etc so in my javascript code im trying to decide which variable amongst them I should manipulate – juria_roberts Commented Sep 4, 2012 at 17:03
• Then don't generate data like that. Generate a JSON literal where the newid is also abstracted out. – user395760 Commented Sep 4, 2012 at 17:04
• It's fine to use it for educational purposes. – SSH This Commented Jul 28, 2018 at 20:05

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2 Answers 2

Sorted by: Reset to default 8

var data1 = { a: 200 };
var newid = 1;
var name = "a";

var varname = "data"+newid+"['"+name+"']";
var value = 3;
eval(varname + "=" + value); // change data1['a'] from 200 to 3

_{Having said that, eval is evil. Are you really sure you need to use dynamic variables?}

Don't use eval. Don't use dynamic variables.

If you have an unordered group of related data, store it in an object.

var myData = {};
myData[ newid + name ] = value;

although it looks like you are dealing with a dynamic object so

myData[ newid ] = myData[ newid ] || {};
myData[ newid ][ name ] = value;

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