Uncaught TypeError: Cannot read property of undefined JSON

Question

I'm working on pulling data from a json object and then displaying the information on the front end. What is the best way to wrap the code below to check to see if the variable SKU is undefined or unavailable then to not run the code at all.

On Google Chrome, I get an Uncaught TypeError: Cannot read property "dm" of undefined based on the code below.

var SKU = "556520000";
var dimBreak = obj[SKU]["dm"];
for(var i = 0; i < dimBreak.length; i++){
    const dimAll = dimBreak[i];
    let entries = Object.entries(dimAll);
    
    for(const [prop, val] of entries) {
        console.log(prop, val);
    }
}

Thanks for your help.

Based on a comment below

I've tried below which gives same error as above.

var dimBreak = obj[SKU]["dm"];
console.log(dimBreak);

if(typeof dimBreak === 'undefined') {
    console.log("Is undefined");
} else {
    console.log("Is defined");
}

This code below however runs

var dimBreak = "Test";
console.log(dimBreak);

if(typeof dimBreak === 'undefined') {
    console.log("Is undefined");
} else {
    console.log("Is defined");
}

Object that is used

{
   "556520000":{
      "lmin":"35",
      "dm":[
         {
            "Width":"147"
         },
         {
            "Depth":"10"
         },
         {
            "Height":"137"
         }
      ],
      "lmax":"68",
   }
}

Does this answer your question? [Detecting an undefined object property](https://stackoverflow.com/questions/27509/detecting-an-undefined-object-property) — Billy Brown, Jul 14 '20 at 13:15
Thanks @BillyBrown but it doesn't seem to work. I've run it in two parts and the latter one runs but the first one throws the same error as above. — user1379695, Jul 14 '20 at 14:01

score 0 · Accepted Answer · answered Jul 14 '20 at 14:11

First you have to check SKU is present in the object, if not add a check. Your code seems to be working(You can see below)

var obj = {
   "556520000":{
      "lmin":"35",
      "dm":[
         {
            "Width":"147"
         },
         {
            "Depth":"10"
         },
         {
            "Height":"137"
         }
      ],
      "lmax":"68",
   }
}

var SKU = "556520000";
if(obj[SKU]){
  var dimBreak = obj[SKU]["dm"];
  for(var i = 0; i < dimBreak.length; i++){
      const dimAll = dimBreak[i];
      let entries = Object.entries(dimAll);

      for(const [prop, val] of entries) {
          console.log(prop, val);
      }
  }
} else {
  console.log(SKU+' is not defined');
}

Uncaught TypeError: Cannot read property of undefined JSON

1 Answers1