How to push string to typescript array?

Question

I am trying to push string to typescript array its throwing error `can not push to undefined" , is it correct way or i need to use spread operator ?

api.ts

const api: IConfigName = {name: "getKey"};
const Name = "Web";

api.optionalParam.push(Name);

IConfig.interface.ts

export interface IConfigName {
    name: string;
    optionalParam?: string[];
}

can not push to undefined is not a real error, please post the actual error message. Are you seeing a runtime JavaScript error, or a compile-time TypeScript error? Are you using strictNullChecks? — Aaron Beall
– Aaron Beall, Commented May 1, 2018 at 17:25

Sajeetharan · Accepted Answer · 2018-05-01 16:27:26Z

5

You need to initialize optionalParam with empty array as follows,

api.optionalParam = [];
api.optionalParam.push(Name);

answered May 1, 2018 at 16:27

Sajeetharan

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1 Comment

Thank you it worked i need to think again i am working with typescript now :)

Nate · Accepted Answer · 2018-05-01 16:29:59Z

2

You are getting this because there is no "optionaParam" defined in your api object.

your api object currently has only one other, which is "name"

to fix, you can add optionalParam like such:

const api: IConfigName = {name: "getKey", optionalParam:[] };
const Name = "Web";

api.optionalParam.push(Name);

this should work, since api now has an optionalParam key, with a type of array.

answered May 1, 2018 at 16:29

Nate

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