[REG: 5.6->5.9]: constructing big JavaScript objects consume huge amounts of memory

Something like:

var dictionaryTable = {};
for (var j = 0; j < 646900; ++j) {
    var word = "a" + j.toString()
    dictionaryTable[word] = null;
}
 

works fine with Qt 5.6, but on 5.9 and newer it consumes all memory (16GB) in sudden spikes. Moreover, it has a serious performance degradation compared to 5.6.