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JavaScript

const resultsReg = []
const resultsTimeout = []
const obj = {
    key : {
        foo: 'bar.jpg'
  }
}

function findImages(object, results) {
  for (var key in object) {
    if (typeof object[key] === 'string') {
      if (object[key].match(/\.(jpg)$/i) && !results.includes(object[key]) && results.length < 9) results.push(object[key]);
    }
    else if (typeof object[key] === 'object') {
      findImages(object[key], results); // this works, but in some applications will give Maximum call stack size exceeded error
    }
  }
}

function findImagesTimeout(object, results) {
  for (var key in object) {
    if (typeof object[key] === 'string') {
      if (object[key].match(/\.(jpg)$/i) && !results.includes(object[key]) && results.length < 9) results.push(object[key]);
    }
    else if (typeof object[key] === 'object') {
      findImagesTimeout(object[key], results);
    }
  }
}

findImages(obj, resultsReg)
findImagesTimeout(obj, resultsTimeout)
console.log(resultsReg)
console.log(resultsTimeout)