@Jaromanda X is correct- you are looking for JSON.parse. Something like this would suffice:

responseArray =  "[{"id":"blah", "type":"blah", ...}, {"id":"blah2",.... },...]"
<Item[]> JSON.parse(responseArray)

Obviously, this doesn't do any validation of the response (which is bad practice). You should ideally perform some validation of the result:

responseArray =  "[{"id":"blah", "type":"blah", ...}, {"id":"blah2",.... },...]"

var result;
try {
   itemListResponse = <Item[]>JSON.parse(responseArray);

   if(!itemListResponse.has("id") ||
      !itemListResponse.has("type") ||
      !itemListResponse.has("state")){

      throw "Invalid Item";
   }
} catch (e){

}

Or, alternatively, use a JSON Schema validator like ajv.

You gave incorrect type to your parsed data. Should be something like this:

interface MyObj {
  name: string
  description: string
}

let obj: { string: MyObj[] } = JSON.parse(data.toString());

So it's not MyObj, it's object with property string containing array of MyObj. Than you can access this data like this:

console.log(obj.string[0].name, obj.string[0].description);

Instead of using anonymous type, you can also define interface for it:

interface MyRootObj {
  string: MyObj[];
}

let obj: MyRootObj = JSON.parse(data.toString());

The interface has an iD field and the json has a date field. They need to be the same types. You also might need to use JSON.parse(stringValue) depending on how you are getting the JSON data.

I think it's because of your mapping in your product class and also the type of your class, try to change class Product to interface Product

like this

    export interface Product{

    public id: number;
    public name: string;
    public category: string;
    public price: number;
    public description: string;
    public currencyCode: string; 

 }

you can go take a look at Angular : Class and Interface for the differences between class and interface

EDIT : (as you can see in my code, I also changed the variable name to match with your JSON response)

There are several problems with your code.

Firstly the json syntax mandates you quote the properties do "val1": "test1" not val1: "test1".

Secondly you should use the import fs = require('fs') syntax for the import.

Thirdly and most importantly, you write the json, as a string to the file. The jsonString is already a string, no need to use stringify on it again. If you do the result of parse will be a string not an object array.

interface MyObj {
    val1: string
    val2: string
    val3: string
}

import fs = require('fs')
const file = 'test.json'
const encode = 'utf8'
const jsonString = '[{"val1" : "test1", "val2" : "test2", "val3" : "test3"}, { "val1" : "test4", "val2" : "test5", "val3" : "test3"}]'
fs.writeFileSync(file, jsonString);
fs.readFile(file, encode, (err, data) => {
    const objs = JSON.parse(data) as MyObj[]
    console.log(data)
    console.log(objs)

    for (const obj of objs) {
        console.log(obj)
        console.log(obj.val1)
        console.log(obj.val2)
        console.log(obj.val3)
    }

})

First of all, I assume the data that you passed into convertData function is not an array. Only Array or Observable have map function in this case. Also, chained function has been changed into pipeable operators in RxJS 6 https://github.com/ReactiveX/rxjs/blob/master/doc/pipeable-operators.md

Secondly, looking at the error message - I don't think the data value returned from the endpoint has value.

Third, data.map(item => {this.serializer.fromJson(item)}); - if the arrow function inside the map function is wrapped in curly bracket, you need to have return keyword. in other word, data.map(item => {this.serializer.fromJson(item)}); should be data.map(item => this.serializer.fromJson(item)); or data.map(item => {return this.serializer.fromJson(item)});

So, what you want to do is to map all the values in the array using <Array>.map. Then you can return the object as an Array in 2 ways, first is using <Object>.values or by just doing [obj.firstName, obj.lastName, obj.age]

You could try Looping through the array and change the values as well using a for loop, but that it really verbose. I'd recommend the 1st approach, since that's more dynamic in this case.

So the resulting code will be

let data = [
  {
    "firstName": "Rajesh",
    "lastName": "Kumar",
    "age": "25"
  },
  {
    "firstName": "john",
    "lastName": "david",
    "age": "26"
  }
];
// I'm assigning the value to the variable called data in this case

data = data.map(item => Object.values(item));

// Now the value of data is the array you want it to be

Now you can follow the other approaches as I specified, however this is the least verbose way to go around.

There are several problems with your code.

Firstly the json syntax mandates you quote the properties do "val1": "test1" not val1: "test1".

Secondly you should use the import fs = require('fs') syntax for the import.

Thirdly and most importantly, you write the json, as a string to the file. The jsonString is already a string, no need to use stringify on it again. If you do the result of parse will be a string not an object array.

interface MyObj {
    val1: string
    val2: string
    val3: string
}

import fs = require('fs')
const file = 'test.json'
const encode = 'utf8'
const jsonString = '[{"val1" : "test1", "val2" : "test2", "val3" : "test3"}, { "val1" : "test4", "val2" : "test5", "val3" : "test3"}]'
fs.writeFileSync(file, jsonString);
fs.readFile(file, encode, (err, data) => {
    const objs = JSON.parse(data) as MyObj[]
    console.log(data)
    console.log(objs)

    for (const obj of objs) {
        console.log(obj)
        console.log(obj.val1)
        console.log(obj.val2)
        console.log(obj.val3)
    }

})