JavaScript“关联”数组访问

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'?

Answer 1

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"];

Answer 2

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?

Answer 3

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

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

alert(bowl.fruit);