Check if Object exists wihout using `if` statement - error: Object is possibly 'undefined'.(2532)

Question

Is there a way to set obj['a32']['a']=3232 without using if statement and without using ! to tell compiler to not check? I tried using ?. but it throws The left-hand side of an assignment expression may not be an optional property access.(2779) Playground: link

interface A{
    [key:string]:{[key:string]:number};
}

const obj:A = {};

const k='a32';
if(!obj[k]){
 obj[k]={};
}

obj[k]['a']=3232; // Object is possibly 'undefined'.(2532)

obj[k]?.['a']=3232; // The left-hand side of an assignment expression may not be an optional property access.(2779)

obj[k]!['a']=3232; // this works but never checks if obj['a32] is defined


if(obj[k]){
    obj[k]['a']=3232;
}

jsejcksn · Accepted Answer · 2021-11-14 02:42:11Z

3

I'm not sure why you want to avoid using an if statement, but you could use the logical nullish assignment operator ??= instead:

TS Playground link

interface A {
  [key: string]: {[key: string]: number};
}

const obj: A = {};

const k = 'a32';

(obj[k] ??= {})['a'] = 3232;

console.log(obj); // { a32: { a: 3232 } }

answered Nov 14, 2021 at 2:42

jsejcksn

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