Iterating JSON object in typescript and adding object to array issue

Question

I have the following JSON object assigned to allDepartments, which is an array of a custom datatype contactItem:

export interface contactItem {
    id : number;
    position: string;
    name : string;
    email : string;
    extension : number;
    phone : Text;
    department: string;
}

public allDepartments: contactItem[];//interface defined in conatctService

This is allDepartmnets:

:

[
    {
        "id": "1",
        "position": "Director of Pathology and Laboratory Medicine",
        "name": "Dr. Niall Swan",
        "email": "[email protected]",
        "extension": "4798",
        "phone": "012214798",
        "department": "General"
    },
    {
        "id": "2",
        "position": "Laboratory Manager",
        "name": "Donal Murphy",
        "email": "[email protected]",
        "extension": "4510",
        "phone": "012124510",
        "department": "General"
    },
    {
        "id": "4",
        "position": "Laboratory Manager",
        "name": "Donal Murphy",
        "email": "[email protected]",
        "extension": "4510",
        "phone": "012124510",
        "department": "General"
    },....

When the department key is equal to biochemistry in an contactItem I want to add the contactItem object to an array of contactItems called biochemistry :

public biochemistry : contactItem[];

//itearte array and assign biochemistry contacts 
   console.log("contacts.page.ts: trting to get biohemistry  data...");

   for (var contact in this.allDepartments){
     console.log("contact = " + this.allDepartments[contact].department);
     if (this.allDepartments[contact].department="biochemistry"){
       this.biochemistry.push(this.allDepartments[contact]);
       console.log("biochem object: " +this.allDepartments[contact]);//array of objects
     }

   }
   })

However an exception is thrown :

TypeError: undefined is not an object (evaluating 'this.biochemistry.push'

The syntax for pushing an object to a Typescript array seems ok, so not sure what the issue is. Any input appreciated.

Sounds like the typing of public biochemistry : contactItem[]; is wrong, and that you're ignoring some TS warnings, but there isn't enough context in the question to see where you're expecting that property to be defined on the instance — CertainPerformance
– CertainPerformance, Commented Apr 10, 2021 at 21:05
As @CertainPerformance said, there is not enough context, but some points: You probably shouldn't use for...in to iterate the array more so because you don't use the index, just use a for...of. Second, you have a typo here if (this.allDepartments[contact].department="biochemistry"){ where you assign "biochemistry" to every department, you need double equals to check for equality(or better use triple equals): if (this.allDepartments[contact].department === "biochemistry"){. — robertgr991
– robertgr991, Commented Apr 10, 2021 at 21:19

dancingbush · Accepted Answer · 2021-04-10 22:35:59Z

1

I had to initialise the array:

public biochemistry : contactItems[] = [];

edited Apr 10, 2021 at 22:35

answered Apr 10, 2021 at 21:46

dancingbush

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