Basically, I am selecting part of the object (values) and I want to inject CreateValue to this object, but with certain condition. I want to check if the field starts with a 'FLD_STR_' and if this field contain an object. I have multiple field 'fld_str_' hence the reason I want to only select the one that contains an object and not a string. I do not think I need to loop in this case. Just add a condition

const values = {
  ID: 748817,
  CODE: "OFFLINE-003",
  FLD_STR_101: {
    field: "FLD_STR_101",
    name: "doc.pdf",
    value: 'base64',
    type: "application/pdf"
  },
  FLD_STR_102: "coucou",
  Table: 109414,
  OWNER: "MJACQUIER",

}
const ele = ()=>{
  if (values.startsWith('FLD_STR_') &&
  typeof values.startsWith('FLD_STR_') === 'object') {
  values.createFileValue = values.startsWith('FLD_STR_');
  
  }
}
console.log(ele())

this is the output :

const values = {
  ID: 748817,
  CODE: "OFFLINE-003",
  FLD_STR_101: {
    field: "FLD_STR_101",
    name: "doc.pdf",
    value: 'base64',
    type: "application/pdf"
  },
  FLD_STR_102: "coucou",
  Table: 109414,
  OWNER: "MJACQUIER",
"createFileValue": {
    field: "FLD_STR_101",
    name: "doc.pdf",
    value: 'base64',
    type: "application/pdf"
  }

}