find the array index of an object with a specific key value in underscore

Question

In underscore  I can successfully find an item with a specific key value  var tv     id 1   id 2   var voteID   2  var data     find tv  function voteItem   return voteItem id    voteID        data     id  2     but how do I find what array index that object occurred at

User · Answer

Array prototype getIndex   function  obj        for  var i   0  i  lt  this length  i              if  this i  Id     obj Id                return i                      return -1     List getIndex obj

User · Answer

I don t know if there is an existing underscore method that does this  but you can achieve the same result with plain javascript   Array prototype getIndexBy   function  name  value        for  var i   0  i  lt  this length  i              if  this i  name     value                return i                      return -1      Then you can just do   var data   tv tv getIndexBy  id   2

User · Answer

If your target environment supports ES2015  or you have a transpile step  eg with Babel   you can use the native Array prototype findIndex     Given your example   const array      id 1    id 2    const desiredId   2  const index   array findIndex obj   gt  obj id     desiredId

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The simplest solution is to use lodash    Install lodash       npm install --save lodash    Use method findIndex    const     require  lodash     findIndexByElementKeyValue    elementKeyValue    gt      return   findIndex array  arrayItem   gt  arrayItem keyelementKeyValue

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Keepin  it simple      Find the index of the first element in array    meeting specified condition     var findIndex   function arr  cond      var i  x    for  i in arr        x   arr i       if  cond x   return parseInt i           var idIsTwo   function x    return x id    2   var tv      id  1    id  2    var i   findIndex tv  idIsTwo     1   Or  for non-haters  the CoffeeScript variant   findIndex    arr  cond  - gt    for i  x of arr     return parseInt i  if cond x

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findIndex was added in 1 8   index     findIndex tv  function voteItem    return voteItem id    voteID      See  http   underscorejs org  findIndex  Alternatively  this also works  if you don t mind making another temporary list   index     indexOf   pluck tv   id    voteId     See  http   underscorejs org  pluck

User · Answer

I got similar case but in contrary is to find the used key based on index of a given object s  I could find solution in underscore using Object values to returns object in to an array to get the occurred index    x000D   x000D  var tv    id1 1 id2 2   x000D  var voteIndex   1  x000D  console log   findKey tv  function item    x000D    return   indexOf Object values tv   item     voteIndex  x000D       x000D   lt script src  https   cdnjs cloudflare com ajax libs underscore js 1 9 1 underscore-min js  gt  lt  script gt  x000D   x000D   x000D

User · Answer

Lo-Dash  which extends Underscore  has findIndex method  that can find the index of a given instance  or by a given predicate  or according to the properties of a given object   In your case  I would do   var index     findIndex tv    id  voteID       Give it a try

User · Answer

you can use indexOf method from lodash  var tv     id 1   id 2   var voteID   2  var data     find tv  function voteItem   return voteItem id    voteID      var index   indexOf tv data

User · Answer

This is to help lodash users  check if your key is present by doing   hideSelectedCompany yourKey     return   findIndex yourArray  n   gt  n     yourKey      -1

User · Answer

If you want to stay with underscore so your predicate function can be more flexible  here are 2 ideas   Method 1  Since the predicate for   find receives both the value and index of an element  you can use side effect to retrieve the index  like this   var idx    find tv  function voteItem  voteIdx       if voteItem id    voteID   idx   voteIdx  return true           Method 2  Looking at underscore source  this is how   find is implemented     find     detect   function obj  predicate  context      var result    any obj  function value  index  list        if  predicate call context  value  index  list           result   value        return true                return result       To make this a findIndex function  simply replace the line result   value  with result   index  This is the same idea as the first method  I included it to point out that underscore uses side effect to implement   find as well

User · Answer

If you re expecting multiple matches and hence need an array to be returned  try     where Users   age  24     If the property value is unique and you need the index of the match  try     findWhere Users    id  10

[javascript] find the array index of an object with a specific key value in underscore

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