ConvertTelerikFilter

let query = "daniel";

let filter = {
  logic: "or",
  filters:[
    { field: "FirstName", operator: "contains", value: query },
    { field: "LastName", operator: "contains", value: query },
    { field: "Email", operator: "contains", value: query },
  ]
}
  
let customFilter = filter.filters
                    .map(f => {
                      return `${f.field}~${f.operator}~'${f.value}'`
                    }).join(`~${filter.logic}~`)
                    ;


console.log(customFilter);