JavaScript "associative" array access

Question

I have a simple simulated array with two elements:

bowl["fruit"] = "apple";
bowl["nuts"] = "brazilian";

I can access the value with an event like this:

onclick = "testButton00_('fruit')">with `testButton00_`

function testButton00_(key){
    var t = bowl[key];
    alert("testButton00_: value = "+t);
}

However, whenever I try to access the array from within code with a key that is just a non-explicit string, I get undefined. Do I have somehow have to pass the parameter with the escaped 'key'?

What do you mean by "just a non-explicit string"?

Guffa
– Guffa

2010-03-26 15:33:07 +00:00
Commented Mar 26, 2010 at 15:33 — Guffa
– Guffa, Commented Mar 26, 2010 at 15:33

Daniel Earwicker · Accepted Answer · 2010-03-26 15:43:17Z

26

The key can be a dynamically computed string. Give an example of something you pass that doesn't work.

Given:

var bowl = {}; // empty object

You can say:

bowl["fruit"] = "apple";

Or:

bowl.fruit = "apple"; // NB. `fruit` is not a string variable here

Or even:

var fruit = "fruit";
bowl[fruit] = "apple"; // now it is a string variable! Note the [ ]

Or if you really want to:

bowl["f" + "r" + "u" + "i" + "t"] = "apple";

Those all have the same effect on the bowl object. And then you can use the corresponding patterns to retrieve values:

var value = bowl["fruit"];
var value = bowl.fruit; // fruit is a hard-coded property name
var value = bowl[fruit]; // fruit must be a variable containing the string "fruit"
var value = bowl["f" + "r" + "u" + "i" + "t"];

edited Mar 26, 2010 at 15:43

answered Mar 26, 2010 at 15:31

Daniel Earwicker

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Comments

Peter Mortensen · Accepted Answer · 2020-08-12 23:17:30Z

1

You could use JSON if you don’t want to escape the key:

var bowl = {
  fruit: "apple",
  nuts: "brazil"
};

alert(bowl.fruit);

edited Aug 12, 2020 at 23:17

Peter Mortensen

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answered Mar 26, 2010 at 15:36

Raj Kaimal

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Comments

Peter Mortensen · Accepted Answer · 2020-08-12 23:16:20Z

0

I am not sure I understand you. You can make sure the key is a string like this

if(!key) {
  return;
}
var k = String(key);
var t = bowl[k];

Or you can check if the key exists:

if(typeof(bowl[key]) !== 'undefined') {
  var t = bowk[key];
}

However, I don't think you have posted the non-working code?

edited Aug 12, 2020 at 23:16

Peter Mortensen

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answered Mar 26, 2010 at 15:35

douwe

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