是否可以在不使用索引号的情况下访问json数组元素？

Question

I have the following JSON:

{
   "responseObject": {
   "name": "ObjectName",
   "fields": [
   {
     "fieldName": "refId",
     "value": "2170gga35511"
   },
   {
     "fieldName": "telNum",
     "value": "4541885881"
   }]}
}

I want to access "value" of the the array element with "fieldName": "telNum" without using index numbers, because I don't know everytime exactly at which place this telNum element will appear.

What I dream of is something like this:

jsonVarName .responseObject.fields['fieldname'='telNum'].value

Is this even possible in JavaScript?

Answer 1

You can do it like this

var k={
   "responseObject": {
   "name": "ObjectName",
   "fields": [
   {
     "fieldName": "refId",
     "value": "2170gga35511"
   },
   {
     "fieldName": "telNum",
     "value": "4541885881"
   }]
}};
value1=k.responseObject.fields.find(
function(i)
{return (i.fieldName=="telNum")}).value;
console.log(value1);

Answer 2

It's not possible.. Native JavaScript has nothing similar to XPATH like in xml to iterate through JSON. You have to loop or use Array.prototype.find() as stated in comments. It's experimental and supported only Chrome 45+, Safari 7.1+, FF 25+. No IE.

Example can be found here

Answer 3

There is JSONPath that lets you write queries just like XPATH does for XML.

$.store.book[*].author  the authors of all books in the store
$..author               all authors
$.store.*               all things in store, which are some books and a red bicycle.
$.store..price          the price of everything in the store.
$..book[2]              the third book
$..book[(@.length-1)] 
$..book[-1:]            the last book in order.
$..book[0,1]
$..book[:2]             the first two books
$..book[?(@.isbn)]      filter all books with isbn number
$..book[?(@.price<10)]  filter all books cheapier than 10
$..*                    All members of JSON structure.

Answer 4

It might be a better option to modify the array into object with fieldName as keys once to avoid using .find over and over again.

fields = Object.assign({}, ...fields.map(field => {
    const newField = {};
    newField[field.fieldName] = field.value;
    return newField;
}

Answer 5

You will have to loop through and find it.

 var json = { "responseObject": { "name": "ObjectName", "fields": [ { "fieldName": "refId", "value": "2170gga35511" }, { "fieldName": "telNum", "value": "4541885881" }] }; function getValueForFieldName(fieldName){ for(var i=0;i<json.fields.length;i++){ if(json.fields[i].fieldName == fieldName){ return json.fields[i].value; } } return false; } console.log(getValueForFieldName("telNum")); 

Answer 6

Clean and easy way to just loop through array.

var json = {
   "responseObject": {
   "name": "ObjectName",
   "fields": [
    {
     "fieldName": "refId",
     "value": "2170gga35511"
    },
  {
    "fieldName": "telNum",
    "value": "4541885881"
  }]
 }   
  $(json.responseObject.fields).each(function (i, field) {
    if (field.fieldName === "telNum") {

      return field.value // break each
    }
  })