Look up property by name using a string variable

Question

I want to look up a property of a Javascript object using a string inside of a variable, but when I execute the code below, the second alert returns undefined.

 <script>
    var operations = {"Create": "POST",
                      "Read": "GET",
                      "Delete": "DELETE"
    };
    //result POST
    alert(operations.Create);

    var method="Create";
    alert(operations.method); //returns undefined, I want it to return "POST"
 </script>

How do I use the "method" variable to look up the "Create" property I created at the beginning of the script?

(The original question has been edited to clarify the author's problem.) — Jon Adams, Mar 01 '12 at 22:32

score 4 · Accepted Answer · answered Feb 09 '12 at 15:41

try

operations[method]

you can't use dot notation if you want to access by a variable. The reason is when you use dot notation, the interpreter is not using the value of the variable; it thinks the variable name itself is the key. In other words, it's looking for the key "method", not "Create".

score 0 · Answer 2 · answered Feb 09 '12 at 15:41

0

Method is not defined in your object declaration so it is doing what it should. var method is not contained within the ooerations. you want to define.

answered Feb 09 '12 at 15:41

thenetimp

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score 0 · Answer 3 · answered Feb 09 '12 at 15:42

Operations does not have a method property. If you wanted to add that value to your object, you could do this:

operations.method = "Create";
alert(operations.method);

If you want to get the value for a specific string key, you can look it up by the indexer:

alert(operations["Create"]);

score 0 · Answer 4 · answered Feb 09 '12 at 15:43

0

You should do:

var method=operations.Create;
alert(method);

or

var method="Create";
alert(operations[method]);

answered Feb 09 '12 at 15:43

Alex Dn

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score 0 · Answer 5 · answered Feb 09 '12 at 15:44

I believe you're declaring method as a separate string object. Instead of

var method="Create";

try doing

operations.method = "Create";

This will make method an actual property of the operations object, which you will be able to access either from operations.method or operations["method"].

score 0 · Answer 6 · answered Feb 09 '12 at 15:44

0

var operations = {"Create" : "POST",
                  "Read" : "GET",
                  "Delete" : "DELETE"
                };

alert(operations.Create);

operations.method = 'Create';
alert(operations.method);

var method = 'Create';
alert(method);

answered Feb 09 '12 at 15:44

osahyoun

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Look up property by name using a string variable

6 Answers6