Calling a variable to reference an array

Question

I am trying to call a string variable to reference an array variable.

message1[0][0] = "Hello."; // existing array
var caller = ['message1', 'message2', 'message3'];

alert(message1[0][0]);

But instead of using the message1 array in the alert, I want to use caller[0] (which is equal to "message1") so that it displays "Hello". How do you do this? This doesn't seem to work:

alert(caller[0][0][0]);

message1[caller[0]], but you really want an plain Object I think. — RobG
– RobG, Commented Jan 1, 2015 at 7:52
Note: You don't call variables. You use them, access them, refer to them, get them, set them... You call functions. — T.J. Crowder
– T.J. Crowder, Commented Jan 1, 2015 at 7:56

T.J. Crowder · Accepted Answer · 2015-01-01 07:52:48Z

2

The best way is to put message1 on an object, then use [] notation to index into the object:

var obj = {
  message1: [
    ["Hello.", "two", "three"]
    ]
};
var caller = ['message1', 'message2', 'message3'];

alert(obj[caller[0]][0][0]);

If message1 is a global variable, it's already on an object — the global object, which you can access as window on browsers. So if it's a global, you could use:

alert(window[caller[0]][0][0]);

But global variables are a Bad Idea^(tm), so best to use your own object instead.

Full disclosure: You can also use eval to do it, but it's a big hammer for a task this small. Just for completeness:

alert(eval(caller[0] + "[0][0]"));

I don't recommend it, but provided you're fully in control of the text you pass into it, it's workable. Much better to use an object, though.

answered Jan 1, 2015 at 7:52

T.J. Crowder

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5 Comments

Mritunjay Over a year ago

The first one is the best way what I think.

T.J. Crowder Over a year ago

And that's why it's first. :-)

ken_vitreous Over a year ago

This is a very good answer, and it already worked as a global variable, but I want to use the object one, and it doesn't seem to work yet. So: message1 starts out as a blank array. My question is, do you declare the array inside the object like this: message1: []?

T.J. Crowder Over a year ago

@ken_vitreous: Yup. It's much the same as an assignment statement, but with a : instead of a =. The bit after the : can be any expression, including an empty array. (That thing is called a "property initialiser"; the {...} thing is an "object initialiser" [sometimes called an "object literal"].) Best,

ken_vitreous Over a year ago

The explanations are very insightful. Thanks a lot!

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