How can I get the index from a JSON object with value?

Question

This is my JSON string.

[{
    "name": "placeHolder",
    "section": "right"
}, {
    "name": "Overview",
    "section": "left"
}, {
    "name": "ByFunction",
    "section": "left"
}, {
    "name": "Time",
    "section": "left"
}, {
    "name": "allFit",
    "section": "left"
}, {
    "name": "allbMatches",
    "section": "left"
}, {
    "name": "allOffers",
    "section": "left"
}, {
    "name": "allInterests",
    "section": "left"
}, {
    "name": "allResponses",
    "section": "left"
}, {
    "name": "divChanged",
    "section": "right"
}]

Now, I have the value allInterests and I want to find out the index (this case; it is '7') of this object in the above string. I tried the following code, but it always returns -1.

var q = MY_JSON_STRING
console.log(q.indexOf( 'allInterests' ) );

Answer 1

You will have to use Array.find or Array.filter or Array.forEach.

Since your value is array and you need the position of the element, you will have to iterate over it.

Array.find

var data = [{"name":"placeHolder","section":"right"},{"name":"Overview","section":"left"},{"name":"ByFunction","section":"left"},{"name":"Time","section":"left"},{"name":"allFit","section":"left"},{"name":"allbMatches","section":"left"},{"name":"allOffers","section":"left"},{"name":"allInterests","section":"left"},{"name":"allResponses","section":"left"},{"name":"divChanged","section":"right"}];
var index = -1;
var val = "allInterests"
var filteredObj = data.find(function(item, i){
  if(item.name === val){
    index = i;
    return i;
  }
});

console.log(index, filteredObj);

Array.findIndex() @Ted Hopp's suggestion

var data = [{"name":"placeHolder","section":"right"},{"name":"Overview","section":"left"},{"name":"ByFunction","section":"left"},{"name":"Time","section":"left"},{"name":"allFit","section":"left"},{"name":"allbMatches","section":"left"},{"name":"allOffers","section":"left"},{"name":"allInterests","section":"left"},{"name":"allResponses","section":"left"},{"name":"divChanged","section":"right"}];

var val = "allInterests"
var index = data.findIndex(function(item, i){
  return item.name === val
});

console.log(index);

Default Array.indexOf() will match searchValue to current element and not its properties. You can refer Array.indexOf - polyfill on MDN

Answer 2

You can use Array.findIndex.

var data= [{
  "name": "placeHolder",
  "section": "right"
}, {
  "name": "Overview",
  "section": "left"
}, {
  "name": "ByFunction",
  "section": "left"
}, {
  "name": "Time",
  "section": "left"
}, {
  "name": "allFit",
  "section": "left"
}, {
  "name": "allbMatches",
  "section": "left"
}, {
  "name": "allOffers",
  "section": "left"
}, {
  "name": "allInterests",
  "section": "left"
}, {
  "name": "allResponses",
  "section": "left"
}, {
  "name": "divChanged",
  "section": "right"
}];
var index = data.findIndex(obj => obj.name=="allInterests");

console.log(index);

Answer 3

In all previous solutions, you must know the name of the attribute or field. A more generic solution for any attribute is this:

let data = 
[{
    "name": "placeHolder",
    "section": "right"
}, {
    "name": "Overview",
    "section": "left"
}, {
    "name": "ByFunction",
    "section": "left"
}, {
    "name": "Time",
    "section": "left"
}, {
    "name": "allFit",
    "section": "left"
}, {
    "name": "allbMatches",
    "section": "left"
}, {
    "name": "allOffers",
    "section": "left"
}, {
    "name": "allInterests",
    "section": "left"
}, {
    "name": "allResponses",
    "section": "left"
}, {
    "name": "divChanged",
    "section": "right"
}]    

function findByKey(key, value) {
    return (item, i) => item[key] === value
}

let findParams = findByKey('name', 'allOffers')
let index = data.findIndex(findParams)

Answer 4

Traverse through the array and find the index of the element which contains a key name and has the value as the passed param.

var data = [{
  "name": "placeHolder",
  "section": "right"
}, {
  "name": "Overview",
  "section": "left"
}, {
  "name": "ByFunction",
  "section": "left"
}, {
  "name": "Time",
  "section": "left"
}, {
  "name": "allFit",
  "section": "left"
}, {
  "name": "allbMatches",
  "section": "left"
}, {
  "name": "allOffers",
  "section": "left"
}, {
  "name": "allInterests",
  "section": "left"
}, {
  "name": "allResponses",
  "section": "left"
}, {
  "name": "divChanged",
  "section": "right"
}];

Array.prototype.getIndexOf = function(el) {

  var arr = this;

  for (var i=0; i<arr.length; i++){
     console.log(arr[i].name);
     if(arr[i].name==el){
       return i;
     }
     
  }
  
  return -1;

}

alert(data.getIndexOf("allResponses"));

Answer 5

Function base solution for get index from a JSON object with value by VanillaJS.

Exemple: https://codepen.io/gmkhussain/pen/mgmEEW

    var data= [{
      "name": "placeHolder",
      "section": "right"
    }, {
      "name": "Overview",
      "section": "left"
    }, {
      "name": "ByFunction",
      "section": "left"
    }, {
      "name": "Time",
      "section": "left"
    }, {
      "name": "allFit",
      "section": "left"
    }, {
      "name": "allbMatches",
      "section": "left"
    }, {
      "name": "allOffers",
      "section": "left"
    }, {
      "name": "allInterests",
      "section": "left"
    }, {
      "name": "allResponses",
      "section": "left"
    }, {
      "name": "divChanged",
      "section": "right"
    }];
    
    
    // create function
    function findIndex(jsonData, findThis){
      var indexNum = jsonData.findIndex(obj => obj.name==findThis);  

    //Output of result
          document.querySelector("#output").innerHTML=indexNum;
          console.log("🍇 Array Index number: " + indexNum + " , value of " + findThis );
    }
    
    
    /* call function */
    findIndex(data, "allOffers");

Output of index number : <h1 id="output"></h1>