CODEWITHSUNDEEP
javascripthtmlarraysobjectecmascript-6
Senthil
Senthil

Reputation: 1101

check if key exist in object javascript

I have object in which if key does not exist set to null using javascript.

If the key doesnot exist in object obj like ccy does not exist cn MY and CA, how to assign and set to null using javascript.

var obj=[{
  "cn": "TH",
  "lang": "thai",
  "bank": "yes",
  "ccy": "THB"
},{
   "cn": "MY",
   "lang": "malay",
},{
   "cn": "CA",
   "lang": "english",
   "bank": "yes"
}]

render(){
  obj.map(e=>
  return html`
    <h1>${e.cn}</h1>
    <h5>${e.lang}</h5>
    <h6>${e.ccy}</h6>
`
 )
}

Upvotes: 3

Views: 147

Answers (6)

aaditya
aaditya

Reputation: 773

var q = [...Object.keys(obj[0]),...Object.keys(obj[1]),...Object.keys(obj[2])]
for(let i=0;i<obj.length;i++){
 for(let k=0;k<q.length;k++){
   if(!(q[k] in obj[i])){
    obj[i][q[k]] = null
  }
 }
}
console.log(obj)

Upvotes: 0

AwesomeGuy
AwesomeGuy

Reputation: 1089

There are multiple ways to check if a given key exists in an object.

if(!obj[0].hasOwnProperty('cn')) {
    obj[o].cn = null
}

or

if(typeof obj[0].cn === 'undefined') {
    obj[0].cn = null;
}

or

if(obj[0].cn === undefined) {
    obj[0].cn = null;
}

The latter two are very similar in this case, typeof is usually used when you want to check if a variable is defined and accessible in the code.

Now the real example is like so:

var missing = ['cn', 'ccy'];
for(var i = 0; i < obj.length; i++) {
    for(var j = 0; j < missing.length; j++) {
        if(!obj[i].hasOwnProperty(missing[j])) {
            obj[i][missing[j]] = null;
        }
    }
}

Upvotes: 0

Ele
Ele

Reputation: 33726

You can use the operator in to check if the key exists as follow:

The operator in is the most secure way for avoiding wrong checks on falsy values.

{"ccy" in e ? e.ccy : null}

Upvotes: 2

dfsq
dfsq

Reputation: 193291

If you don't want to write default fallback values into template and want to keep template clean, you could also preprocess data and set missing values before rendering:

var obj = [{
  "cn": "TH",
  "lang": "thai",
  "bank": "yes",
  "ccy": "THB"
}, {
  "cn": "MY",
  "lang": "malay",
}, {
  "lang": "english",
  "bank": "yes"
}]

obj = obj.map(({
  cn = null,
  ccy = null,
  ...rest
}) => Object.assign(rest, { cn, ccy }))

console.log(obj)

Upvotes: 3

Albin w&#228;rme
Albin w&#228;rme

Reputation: 261

Any key not defined in a javascript object will be considered to be undefined so you could either check 

(typeof obj.ccy === "undefined") ? null : obj.ccy;
(obj.ccy == undefined) ? null : obj.ccy;

If you are not familiar with ternary expressions. You could also write the above as this. 

if(obj.ccy == undefined){
   obj.ccy = null;
}

Upvotes: 0

Jack Bashford
Jack Bashford

Reputation: 44125

The easiest thing to do, as long as you can be sure e.ccy won't be falsy (false, undefined, null, 0, "", or NaN) is to use the logical OR operator ||:

${e.ccy || null}

Upvotes: 4

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