Javascript/jquery: Get Key By Value Inside A Nested Array

var myJSON = {'data': [{'obj1':'value1', 'obj2':'value2'}, {'obj1':'value3', 'obj2':'value4'}, {'obj1':'value5', 'obj2':'value6'}] }; I've g

Solution 1:

I'm guessing the way to solve this is to figure out what the i should be in data[i] for value4 and then simply call data[i].obj1.

obj2, you mean, not obj1.

But how do I get that i?

You search for it. It's a simple loop.

var i;
for (i = 0; i < myJSON.data.length; ++i) {
    if (myJSON.data[i].obj2 === "value4") {
        // Found itbreak;
    }
}
if (i < myJSON.data.length) {
    // Found it, it's at index `i`
}

Or on a system where you can rely on ES5's forEach (either because the engine has it natively, or because you've added a shim):

var i;
myJSON.data.forEach(function(entry, index) {
    if (entry.obj2 === "value4") {
        i = index;
    }
};
if (typeof i !== "undefined") {
    // Found it
}

You can't stop a forEach early, so that does some unnecessary looping. You could use some:

var i;
myJSON.data.some(function(entry, index) {
    if (entry.obj2 === "value4") {
        i = index;
        returntrue; // Stops loop
    }
};
if (typeof i !== "undefined") {
    // Found it
}

Solution 2:

Try this simple recursive function:

find = function(where, what) {
    if (typeof where != "object")
        returnnull;
    var matches = true;
    for (var p in what)
        matches = matches && (where[p] == what[p]);
    if (matches)
        returnwhere;
    for (var p inwhere) {
        var found = find(where[p], what);
        if(found)
            return found;
    }
    returnnull;
}

It works with objects of any depth and allows for multiple search keys. For your example:

vardata = {"data":
        [{"obj1":"value1",
            "obj2":"value2"},

            {"obj1":"value3",
                "obj2":"value4"},

            {"obj1":"value5",
                "obj2":"value6"}]
};

result = find(data, {"obj2":"value4"})
console.log(result.obj1) // value3

Another (and nicer) way to do the same is to provide a test predicate for the finder function:

find = function(where, test) {
    if (test(where))
        returnwhere;
    if (typeof where != "object")
        returnnull;
    for (var p inwhere) {
        var found = find(where[p], test);
        if (found)
            return found;
    }
    returnnull;
}

result = find(data, function(x) { return x.obj2 == "value4" });

Solution 3:

You'll have to manually trawl through your object:

for(var a=0; a<myJSON.data.length; a++)
{
 for(var b in myJSON.data[a])
 {
  if(myJSON.data[a][b]=="value4")
  {
   console.log("myJSON["+a+"]."+b)
  }
 }
}

Solution 4:

I would recommend to revise the entire data-structure, but assume that this is an abstracted example.

for(var ei in myJSON["data"]){
    if (myJSON["data"][ei]['obj2'] == "value4")){
      //ei contains the key
      //do something & break;
    }
}

Here is one-liner, although slower:

myJSON["data"].map(function(e,i){if(e["obj2"]=="value4")return e;}).filter(Boolean)[0];

or for the key:

myJSON["data"].map(function(e,i){if(e["obj2"]=="value4")return i;}).filter(Number)[0];

Also see T.J. Crowders answer using some - still slow but avoiding unnecessary cycles.

Solution 5:

If you are using jQuery then you could use the grep function to perform your search:

var searchValue = "value4";

var result = $.grep(myJSON.data, function (e) { 
        return e.obj2 === searchValue;
    });

console.log(result[0].obj1);

See here for a working example.