JSON/Javascript: return INDEX of array object containing a certain property

Question

Given a JSON object such as this:

{
  "something": {
    "terms": [
      {
        "span": [
          15,
          16
        ],
        "value": ":",
        "label": "separator"
      },
      {
        "span": [
          16,
          20
        ],
        "value": "12.5",
        "label": "number"
      }
    ],
    "span": [
      15,
      20
    ],
    "weight": 0.005,
    "value": ":12.5"
  }
 }

I asked a question about parsing the object out where label: number here: JSON/Javascript: return which array object contains a certain property

I got a sufficient answer there (use filter()), but now need to know the original index of the object.

This issue seems to have the answer, but I simply don't know enough about javascript to translate it into something useful for my particular problem.

The following code successfully returns the object. Now I need to modify this to return the original index of the object:

var numberValue, list = parsed.something.terms.filter(function(a){
  return a.label==='number';
});
numberValue = list.length ? list[0].value : -1;

This needs to be a pure javascript solution, no external libraries, etc.

What you want to acheive ? what you expect from answer ? an example please. — Zakaria Acharki
– Zakaria Acharki, Commented Aug 2, 2015 at 14:38
@ZakariaAcharki Not sure what you mean. The only thing I need returned is the index of the original object. This is requested in my question and is achieved by the approved answer. Is there something specific I needed to do in order to make this question better? Happy to do so if needed. — dtburgess
– dtburgess, Commented Aug 2, 2015 at 14:50

sheilak · Accepted Answer · 2015-08-02 14:48:33Z

3

I don't think you can modify the filter solution as within the filter you've lost the indexes.

The solution you've linked to uses the angular external library.

So here is a pure JS solution:

var numberValue = parsed.something.terms
    .map(function(d){ return d['label']; })
    .indexOf('number');

Array.prototype.indexOf()

Array.prototype.map()

edited Aug 2, 2015 at 14:48

answered Aug 2, 2015 at 14:32

sheilak

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4 Comments

frenchie Over a year ago

indexOf doesn't work in IE8, which may or may not be a big deal. The OP should make sure to add this function to the array prototype.

sheilak Over a year ago

Yeah I assumed that since filter was already being used that map/indexOf would be OK

ttzn Over a year ago

@frenchie, well, neither does filter.

dtburgess Over a year ago

Thanks. IE8 compatibility is not needed. OP

ttzn · Accepted Answer · 2015-08-02 14:34:25Z

1

Use forEach and collect the indices of objects that satisfy the a.label==='number' predicate :

var target = parsed.something.terms;
var list = [];
target.forEach(function(element, index){
    if (element.label==='number') {
        list.push(index)
    };
});
var numberValue = list.length ? target[list[0]].value : -1;

console.log(list); // [1]
console.log(numberValue); // 12.5

answered Aug 2, 2015 at 14:34

ttzn

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