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JSON.stringify not working for all properties of object in Typescript
JSON.stringify not working for all properties of the outermost object in Typescript.
Please refer to code snippet below:
class Criterion {
    '@CLASS' = 'xyz.abc.Criterion'
    operator: string;
    operand: string[];
    field: string;
    constructor(field:string,operator:string,operand: string[]) {
      this.field = field;
      this.operator = operator;
      this.operand = operand;
    }
}

class Filter {
    '@CLASS': 'xyz.ada.Filter';
    criteria: Criterion[];
    constructor(criteria:Criterion[]) {
        this.criteria=criteria;
    }
}

var criterion = new Criterion("a","b",["c"]);
var a = new Filter([criterion]);
JSON.stringify(a);
console.log(JSON.stringify(a));

Output:
{"criteria":[{"@CLASS":"xyz.abc.Criterion","field":"a","operator":"b","operand":["c"]}]}

Expected:
{"@CLASS":"xyz.ada.Filter","criteria":[{"@CLASS":"xyz.abc.Criterion","field":"a","operator":"b","operand":["c"]}]}

It is not stringifying the @CLASS property of the Filter class object.
code link

There is a typo in your class filter. Replace the two dots with:
'@CLASS'= 'xyz.ada.Filter';

